1884 

ANEROID  BAROMETER: 


ITS 


CONSTR  jCTION  AND  OSb, 


R  Z  V 


NL V    \ORK : 

D.   VAN   NOSTBANT)   COMPANY, 

23  MURRAY  AND  27  WARREN  C  REET. 
1893. 


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THE 

ANEROID  BAROMETER: 

ITS 

CONSTRUCTION  AND  USE. 


>  • 


THIKD     EDITION. 

REVISED    AND    ENLAROED. 


NEW  YORK: 

D.  VAN  NOSTRAND   COMPANY, 

23  MURRAY  AND  27  WARREN  STREET. 

1890. 


COPYRIGHT,  1884, 
BY  D.  VAN  NOSTRAND. 


CONTENTS. 


PAGE. 

CHAPTER  I.  — Th  e  Atmosphere 5 

CHAPTER  II. — Barometric     Measurements 

of  Altitudes 27 

CHAPTER  III. — Aneroid  Barometers :  Their 

Construction 39 

CHAPTER  IY. — The  Use  of  Aneroid  Bar- 
ometers i .  x.v .  * 52 

CHAPTER  V. — Suggestions  in  Regard  to 
the  Selection  and  Systematic  Use  of 

an  Aneroid 77 

TABLE  L—  Prof .  Airy's  Table  of  Altitudes.     88 

TABLE  II. — Logarithmic  Table 106 

TABLE  III —Metric  Altitude  Table 121 

TABLE  IV — Corrections  for  Mercurial  Bar- 
ometer   125 

TABLE  V. — Boiling  Point  of  Water  cor- 
responding to  Different  Barometric 
Pressures...  .  126 


PREFACE  TO   SECOND  EDITION. 


THE  fact  that  the  first  edition  of  this 
little  manual  is  entirely  exhausted  is  a 
sufficient  indication  that  it  supplied  a 
want.  As  the  use  of  the  Aneroid  Bar- 
ometer is  on  the  increase,  the  presump- 
tion is  that  there  will  be  a  further 
demand  for  this  book  of  tables  and  in- 
structions. 

It  has  been  thought  advisable  to  re- 
arrange the  matter  and  to  increase  it 
by  fuller  descriptions  of  different  in- 
struments ;  and  what  is  of  more  im- 
portance to  the  novice  in  measuring 
altitudes,  to  add  a  number  of  ex- 
amples. 

Another  table  has  also  been  added  to 
the  collection  of  the  previous  edition. 


THE  ANEROID  BAROMETER; 

ITS   CONSTRUCTION  AND  USE. 


CHAPTEK  I. 

TH*E      ATMOSPHERE. 

The  gaseous  envelope  which  surrounds 
oar  globe,  and  to  which  we  give  the 
name  of  atmosphere,  is  subject  to  many 
and  varied  changes.  In  the  relative 
amount  of  the  two  gases  which  chiefly 
compose  it,  it  remains  marvelously  con- 
stant; yielding  upon  analysis  the  same 
ratio  of  oxygen  to  nitrogen  for  all  lati- 
tudes and  all  altitudes.  It  is  only  within 
a  few  restricted  and  generally  confined 
areas  where  the  natural  chemical  pro- 
cesses of  respiration,  combustion  or  fer- 
mentation are  active,  that  the  free  oxy- 
gen is  found  to  be  notably  deficient,  and 
the  product,  carbonic  dioxide,  which  ex- 
ists normally  to  the  extent  of  one  twen- 


G 


ty-fifth  of  one  per  cent.,  is,  to  a  corre- 
sponding extent,  in  excess. 

When,  however,  we  regard  the  condi- 
tions which  arise  from  its  physical  prop- 
erties, no  such  constancy  is  observable. 
Indeed,  it  seems  the  most  fitting  type  of 
a  transitory  state,  and  whether  we  regard 
the  temperature,  the  moisture,  the  press- 
ure resulting  from  its  weight,  or  the  di- 
rection and  velocity  of  its  motions,  we 
can  only  acquaint  ourselves  with  the 
lire  its  within  which  these  conditions  have 
been  known  to  vary.  The  nature  of 
the  changes  within  these  limits  we  can- 
not, in  the  present  state  of  our  knowl- 
edge, assume  to  predict  for  the  future, 
except  for  very  limited  periods;  and  even 
then  the  prediction  is  set  forth  only  as  a 
"probability." 

Certain  average  conditions  are  noticea- 
ble as  belonging  to  certain  areas  or  zones 
of  the  earth,  and  differing  somewhat 
among  themselves,  especially  as  to 
greater  or  less  range  in  temperature, 
moisture,  etc.  To  such  general  condi- 
tions we  apply  the  term  climate. 


The  department  of  science  which  re- 
gards the  physical  phenomena  arising 
from  these  varying  conditions  is  called 
meteorology.  The  instruments  employed 
with  which  to  indicate  or  measure  the 
extent  of  these  changes,  are  of  various 
kinds.  Thus  the  thermometer  indicates 
the  relative  temperature,  the  hygrometer 
the  humidity,  the  anemometer  the  force 
or  the  velocity  of  the  wind,  and  the  bar- 
ometer the  pressure  of  the  air  which 
arises  directly  from  its  weight. 

It  is  with  the  last  of  these  instruments 
that  we  are  especially  concerned  in  the 
present  essay.  It  has  two  quite  distinct 
uses  :  One  to  indicate  the  varying  press- 
ures of  the  air  at  some  fixed  point  for 
meteorological  purposes,  and  the  other 
to  indicate  difference  in  altitude  of  points 
to  which  the  instrument  is  carried  by  af- 
fording a  measure  of  the  greater  or  less 
amount  of  atmosphere  above  it.  Before 
using  the  instrument  to  measure  alti- 
tudes it  is  important  to  become  some- 
what familiar  with  its  use  as  a  stationary 
instrument.  The  barometer  most  fre- 


8 


quently  employed  for  such  use  is  the  one 
invented  by  Tcricelli  in  1643.  It  is  too 
well  known  to  require  description  here. 
It  will  be  sufficient  to  say  that  it  meas- 
ures the  varying  pressure  of  the  air  by 
the  varying  length  of  a  column  of  mer- 
cury which  balances  the  pressure. 

When  the  barometer  is  employed  for 
the  purposes  of  meteorology  only,  the 
following  facts  are  taken  into  considera- 
tion. We  quote  from  Buchan's  "  Handy 
Book  of  Meteorology." 

Variations  of  the  Jlarometer. — The 
variations  observed  in  the  pressure  of 
the  air  may  be  divided  into  two  classes, 
viz.,  periodical  and  irregular ;  the  peri- 
odical variations  recurring  at  regular  in- 
tervals, whilst  the  irregular  variations 
observe  no  stated  times.  The  most 
marked  of  the  periodical  variation  is  the 
daily  variation,  the  regularity  of  which 
in  the  tropics  is  so  great  that,  according 
to  Humboldt,  the  hour  may  be  ascer- 
tained from  the  height  of  the  barometer 
without  an  error  of  more  than  15  or  17 
minutes  on  the  average.  This  horary 


oscillation  of  the  barometer  is  masked  in 
Great  Britain  by  the  frequent  fluctuations 
to  which  the  atmosphere  is  subjected  in 
these  regions.  It  is,  however,  detected 
by  taking  the  mean  of  a  series  of  hourly 
observations  conducted  for  some  time. 
The  results  show  two  maxima  occurring 
from  9  to  11  A.M.  and  from  9  to  11  P.M., 
and  two  minima  occurring  from  3  to  5 
A.M.  and  from  3  to  5  P.M.  (See  Table, 
page  10.) 

The  maxima  occur  when  the  tempera- 
ture is  about  the  mean  of  the  day,  and 
the  minima  when  it  is  at  the  highest  and 
lowest  respectively. 

This  daily  fluctuation  of  the  barometer 
is  caused  by  the  changes  which  take 
place  from  hour  to  hour  of  the  day  in 
the  temperature,  and  by  the  varying 
quantity  of  vapor  in  the  atmosphere. 

The  surface  of  the  globe  is  always 
divided  into  a  day  and  night  hemisphere, 
separated  by  a  great  circle  which  revolves 
with  the  sun  from  east  to  west  in  twenty- 
four  hours.  These  two  hemispheres  are 
thus  in  direct  contrast  to  each  other  in 


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respect  of  heat  and  evaporation.  The 
hemisphere  exposed  to  the  sun  is  warm, 
and  that  turned  in  the  other  direction  is 
cold.  Owing  to  the  short  time  in  which 
each  revolution  takes  place,  the  time  of 
greatest  heat  is  not  at  noon,  when  the  sun 
is  in  the  meridian,  but  about  two  or  three 
hours  thereafter ;  similarly,  the  period  of 
greatest  cold  occurs  about  four  in  the 
morning.  As  the  hemisphere  under  the 
sun's  rays  becomes  heated,  the  air,  ex- 
panding upwards  and  outwards,  flows 
over  upon  the  other  hemisphere  where 
the  air  is  colder  and  denser.  There  thus 
revolves  round  the  globe  from  day  to  day, 
a  wave  of  heat,  from  the  crest  of  which 
air  constantly  tends  to  flow  towards  the 
meridian  of  greatest  cold  on  the  opposite 
side  of  the  globe. 

The  barometer  is  influenced  to  a  large 
extent  by  the  elastic  force  of  the  vapor 
of  water  invisibly  suspended  in  the  at- 
mosphere, in  the  same  way  as  it  is  influ- 
enced by  the  dry  air  (oxygen  and  hydro- 
gen). But  the  vapor  of  water  also 
exerts  a  pressure  on  the  barometer  in 


12 

another  way.  Vapor  tends  to  diffuse 
itself  equally  through  the  air ;  but  as  the 
particles  of  air  offer  an  obstruction  to  the 
watery  particles,  about  9  or  10  A.M.,  when 
evaporation  is  most  rapid,  the  vapor  is 
accumulated  or  pent  up  in  the  lower 
stratum  of  the  atmosphere,  and  being 
impeded  in  its  ascent  its  elastic  force  is 
increased  by  the  reaction,  and  the  barom- 
eter consequently  rises.  When  the  air 
falls  below  the  temperature  of  the  dew- 
point,  part  of  its  moisture  is  deposited 
in  dew,  and  since  some  time  must  elapse 
before  the  vapor  of  the  upper  strata  can 
diffuse  itself  downwards  to  supply  the 
deficiency,  the  barometer  falls — most 
markedly  at  10  P.M.,  when  the  deposition 
of  dew  is  greatest. 

Hence,  as  regards  temperature,  the 
barometer  is  subject  to  a  maximum  and 
minimum  pressure  each  day — the  maxi- 
mum occurring  at  the  period  of  greatest 
cold,  and  the  minimum  at  the  period  of 
greatest  heat.  And  as  regards  vapor  in 
the  atmosphere,  the  barometer  is  subject 
to  two  maxima  and  minima  of  pressure — 


13 

the  maxima  occurring  at  10  A.M.,  when, 
owing  to  the  rapid  evaporation,  the  accu- 
mulation of  vapor  near  the  surface  is 
greatest,  and  about  sunset,  or  just  be- 
fore dew  begins  to  be  deposited,  when 
the  relative  amount  of  vapor  is  great ; 
and  the  minima  in  the  evening,  when  the 
deposition  of  dew  is  greatest,  and  before 
sunrise,  when  evaporation  and  the  quan- 
tity of  vapor  in  the  air  is  least. 

Thus  the  maximum  in  the  forenoon  is 
brought  about  by  the  rapid  evaporation 
arising  from  the  dryness  of  the  air  and 
the  increasing  temperature.  But  as  the 
vapor  becomes  more  equally  diffused, 
and  the  air  more  saturated,  evaporation 
proceeds  more  languidly  ;  the  air  becomes 
also  more  expanded  by  the  heat,  and 
flows  away  to  meet  the  diurnal  wave  of 
cold  advancing  from  the  eastwards. 
Thus  the  pressure  falls  to  the  afternoon 
minimum  about  4  P.M.  From  this  time 
the  temperature  declines,  the  air  ap- 
proaches more  nearly  the  point  of  satu- 
ration, and  the  pressure  being  further 
increased  by  accessions  of  air  from  the 


14 

warm  wave,  now  considerably  to  the 
westward,  the  evening  maximum  is  at- 
tained. As  the  deposition  of  dew  pro- 
ceeds, the  air  becomes  drier,  the  elastic 
pressure  of  the  vapor  is  greatly  dimin- 
ished, and  the  pressure  falls  to  a  second 
minimum  about  4  A.M. 

The  amount  of  these  daily  variations 
diminishes  from  the  equator  towards 
either  pole,  for  the  obvious  reason  that 
they  depend,  directly,  or  indirectly,  on 
the  heating  power  of  the  sun's  rays. 
Thus,  while  at  the  equator  the  daily  fluc- 
tuation is  0.125  inch,  in  Great  Britain  it 
is  only  a  sixth  part  of  that  amount.  It 
is  very  small  in  the  high  latitudes  of  St. 
Petersburg  and  Bossekop ;  and  in  still 
higher  latitudes,  at  that  period  of  the 
year  when  there  is  no  alternation  of  day 
and  night,  the  diurnal  variation  probably 
does  not  occur.  In  the  dry  climate  of 
Barnaul,  in  Siberia,  there  is  no  evening 
maximum ;  the  lowest  minimum  occurs 
as  early  as  midnight,  and  the  only  maxi- 
mum at  9  A.  M. 

Since    the   whole    column    of    the    at- 


15 

mosphere,  from  the  sea-level  upwards, 
expands  during  the  heat  of  the  day,  thus 
lifting  a  portion  of  it  above  all  places  at 
higher  levels,  it  is  evident  that  the  after- 
noon minimum  at  high  stations  will  be 
less  than  at  lower  stations,  especially 
when  the  ascent  from  the  one  to  the  oth- 
er is  abrupt.  Thus,  at  Padua,  in  Italy, 
the  afternoon  minimum  is  0.014  inch,  but 
at  Great  St.  Bernard  it  is  only  0.003 
inch. 

Annual  Variation. — When  it  is  sum- 
mer in  the  one  hemisphere,  it  is  winter 
in  the  other.  In  the  hemisphere  where 
summer  prevails,  the  whole  air  being 
warmer  than  in  the  other  hemisphere, 
expands  both  vertically  and  laterally.  As 
a  consequence  of  the  lateral  expansion 
there  follows  a  transference  of  part  of 
the  air  from  the  warm  to  the  cold  hemi- 
sphere along  the  earth's  surface ;  and,  as 
a  consequence  of  the  vertical  expansion, 
an  overflow  in  the  upper  regions  of  the  at- 
mosphere in  the  same  direction.  Hence, 
in  so  far  as  the  dry  air  of  the  atmosphere 
is  concerned,  the  atmospheric  pressure 


16 


will  be  least  in  the  summer  and  greatest 
in  the  winter  of  each  hemisphere.  But 
the  production  of  aqueous  vapor  by  evap- 
oration being  most  active  in  summer,  the 
pressure  on  the  barometer  will  be  much 
increased  from  this  cause.  As  the  aque- 
ous vapor  is  transferred  to  the  colder 
hemisphere  it  will  be  there  condensed 
into  rain,  and  being  thereby  withdrawn 
from  the  atmosphere,  the  barometer 
pressure  will  be  diminished  ;  but  the  dry 
air  which  the  vapor  brought  with  it  from 
the  warm  hemisphere  will  remain,  thus 
tending  to  increase  the  pressure. 

In  the  neighborhood  of  the  equator 
there  is  little  variation  in  the  mean  press- 
ure from  month  to  month.  Thus,  at 
Cayenne,  the  pressure  in  January  is 
29.903  inches,  and  in  July  29.957 
inches. 

At  Calcutta,  22°  36 '  N.  lat.,  the  press- 
ure is  29.408  in  July,  and  30.102  in  Jan- 
uary, thus  showing  a  difference  of  0.694; 
tind  at  Bio  de  Janeiro,  22°  57'  S.  lat.,  it 
is  29.744  in  January  (summer),  and  29.978 
in  July  (winter),  the  difference  being 


17 

0.234.  The  large  annual  variation  at 
Calcutta  is  caused  jointly  by  the  great 
heat  in  July,  and  by  the  heavy  rains 
which  accompany  the  south-west  mon- 
soons at  this  season ;  while  in  January 
the  barometer  is  high,  owing  to  the 
north-east  monsoons,  by  which  the  dry 
cold  dense  air  of  Central  Asia  is  con- 
veyed southward  over  India. 

At  places  where  the  amount  of  vapor  in 
the  air  varies  little  from  month  to  month, 
but  the  variations  of  temperature  are 
great,  the  difference  between  the  summer 
and  winter  pressures  are  very  striking. 
Thus,  at  Barnaul  and  Irkutsk,  both  in 
Siberia,  the  pressures  in  July  are  respect- 
ively 29.243  and  28.267,  and  in  January 
29.897  and  28.865,  the  differences  being 
upwards  of  six-tenths  of  an  inch.  The 
great  heat  of  Siberia  during  summer 
causes  the  air  to  expand  and  flow  away 
in  all  directions,  and  the  diminished 
pressure  is  not  compensated  for  by  any 
material  accessions  being  made  to  the 
aqueous  vapor  of  the  atmosphere ;  and, 
on  the  other  hand,  the  great  cold  and 


18 

little  rain  in  that  region  during  winter 
causes  high  pressures  to  prevail  during 
that  season.  The  same  peculiarity  is 
seen,  though  in  a  modified  degree,  at 
Moscow,  St.  Petersburg,  and  Vienna. 

At  Reykjavik,  in  Iceland,  the  pressure 
in  June  is  29.717,  and  in  December 
29.273;  at  Sandwich,  Orkney,  29.77  ~. 
and  29.586;  and  at  Sitcha,  in  Russian 
America,  29.975,  and  29.664.  In  all 
these  places  the  distribution  of  the  press- 
ure is  just  the  reverse  of  what  obtains  in 
Siberia,  being  least  in  winter  and  great- 
est in  summer.  The  high  summer  press- 
ures are  due  to  the  cool  summer  tem- 
peratures as  compared  with  surrounding 
countries,  thus  causing  an  inflow  from 
these  region*,  and  to  the  large  amount  of 
vapor  in  the  atmosphere,  thus  still  fur- 
ther raising  the  barometric  column.  On 
the  other  hand,  the  low  winter  pressu 
are  due  to  the  comparatively  high  winter 
temperatures  causing  an  outflow  towards 
adjoining  countries,  and  the  large  winter 
rainfall  which,  by  setting  free  great  quan- 


19 

'8  of  latent  heat,  still  farther  aug- 
ments and  accelerates  the  outflow. 

The  variations  in  mean  pressure  are 
very  slight,  and  not  marked  by  any  very 
decided  regularity  in  their  march  through 
the  seasons,  at  Dublin,  Glasgow,  London, 
Paris,  and  Rome.  As  compared  with 
Barnaul  and  Reykjavik  their  temperature 
is  at  no  season  very  different  from  that 
of  surrounding  countries,  and  the  vapor 
and  rainfall  are  at  no  time  much  in  excess 
or  defect,  but  are  more  equally  distrib- 
uted over  the  different  months  of  the 
year. 

At  the  Great  St  Bernard,  8174  feet 
above  the  sea,  the  pressure  in  summer  is 
--'  :*64  inches,  while  in  winter  it  is  only 
22.044.  At  Padua,  there  is  scarcely  any 
difference  in  the  pressure  between  sum- 
mer and  winter.  The  increase  in  the 
summer  pressure  at  the  Great  St  Ber- 
nard is  no  doubt  due  to  the  same  cause 
already  referred  to  in  art.  65 — viz.,  the 
expansion  of  the  air  upward  during  the 
warm  summer  months,  thus  raising  a 
larger  portion  of  it  above  the  barometer 


20 


at  the  highest  station.  But  at  St.  Fe  de 
Bogota,  8615  feet  high,  near  the  equator, 
and  where,  consequently,  the  difference 
between  the  temperature  in  July  and 
January  is  very  small,  the  difference  in 
the  pressures  of  the  same  months  is  also 
very  small,  being  only  0.035. 

Distribution  of  Atmospheric,  Press- 
ure over  the  globe,  as  determined  by  the 
Annual  Means. — Though  much  addi- 
tional observation  is  required,  especially 
in  Africa,  Asia,  and  South  America,  be- 
fore the  isobarometric  lines  can  be  laid 
down  on  a  map  of  the  world,  yet  many 
important  conclusions  regarding  the 
mean  barometric  pressure  have  been  ar- 
rived at  from  the  results  already  obtained. 
We  have  seen  that  the  daily  and  monthly 
variations  of  pressure  observed  at  differ- 
ent places  are  modified  by  the  variations 
of  the  temperature  of  the  air,  the  amount 
of  vapor,  and  the  rainfall.  Since  these 
are  in  their  turn  greatly  modified  by  the 
unequal  distribution  of  land  and  water 
on  the  earth's  surface,  we  should  expect 
to  find  the  pressure,  and  the  variations 


21 


in  the  pressure,  most  regular  in  the 
southern  hemisphere.  Accordingly,  there 
is  a  remarkable  regularity  observed  in 
the  distribution  of  the  pressure  from 
about  40°  N.  lat.  southwards  to  the  Ant- 
arctic Ocean,  with  the  exception  of  the 
region  of  the  monsoons  in  Southern  Asia. 

The  mean  pressure  in  the  equatorial 
regions  is  about  29.90;  at  20°  N.  lat.  it 
rises  to  30.00,  and  at  35°  N.  lat.  to  30.20, 
from  which  northwards  the  pressure  is 
diminished.  The  same  peculiarity  is  seen 
south  of  the  equator,  but  it  is  not  so 
strongly  marked.  At  45°  S.  lat.  it  falls 
to  29.90,  and  from  this  southwards  it 
continues  steadily  and  rapidly  to  fall  to  a 
mean  pressure  of  28.91  at  75°  S.  lat. 
This  extraordinary  depression  of  the 
barometer  in  the  Antartic  Ocean,  being 
one  inch  less  than  at  the  equator  and 
1,326  inches  less  than  at  Algiers,  is  per- 
haps the  most  remarkable  fact  in  the 
meteorology  of  the  globe. 

The  pressure  in  the  north  temperate 
and  frigid  zones  is  in  striking  contrast  to 
the  above.  From  Athens,  in  a  north- 


22 

eastern  direction,  a  high  isobarometric 
line  traverses  Asia,  passing  in  its  course 
Tim's,  Barnaul,  Irkutsk,  and  Yakutsk. 
To  the  east  of  the  northern  part  of  this 
area  of  high  mean  pressure,  around  the 
peninsula  of  Kamtschatka,  there  is  a 
region  of  low  barometer,  the  mean  press- 
ure being  only  29.682.  There  is  another 
remarkable  area  of  low  pressure  around 
Iceland,  the  center  being  probably  in  the 
south-west  of  the  island  near  Reykjavik, 
where  the  mean  is  29.578.  As  observa- 
tions are  more  numerous  in  Europe  and 
North  America,  the  dimensions  of  this 
depression  may  be  defined  with  consider- 
able precision  by  drawing  the  isobaro- 
metric of  29.90,  which  is  about  the  mean 
atmospheric  pressure.  This  line  passes 
through  Barrow  Straits  in  North  Amer- 
ica, thence  south-eastward  toward  New- 
foundland, then  eastward  through  the 
north  of  Ireland,  the  south  of  Scotland, 
and  the  south  of  Sweden,  whence  it  pro- 
ceeds in  a  north-easterly  direction  to 
Spitzbergen.  The  following  mean  annual 
pressures  will  show  the  nature  of  the  de- 


23 


pression :  New  York,  30.001 ;  Paris, 
29.988;  London,  29.956;  Glasgow,  29.863; 
Orkney,  29.781;  Bergen,  29.804;  Spitz- 
bergen,  29.794;  Keykjavik,  29.578;  God- 
thaab,  in  S.  Greenland,  29.605;  Uperna- 
vik,  in  N.  Greenland,  29.732 ;  and  Mel- 
ville  Island,  29.807.  A  depression  also 
occurs  in  India,  where  the  mean  is  only 
about  29.850,  whereas  in  the  same  lati- 
tudes elsewhere  it  is  about  30.100. 

There  are  thus  four  areas  of  low  press- 
ure on  the  globe,  the  extent  of  each  being 
nearly  proportioned  to  the  depth  of  the 
central  depression — viz.,  Antarctic  Ocean, 
the  least  pressure  being  28.910  ;  Iceland, 
29.578  ;  Kamtschatka,  29.682 ;  and  India, 
29.850 ;  and  three  areas  of  high  pressure, 
one  lying  between  latitudes  20°  and  40° 
N.,  another  between  15°  and  35°  S.,  and 
the  third  in  Central  Asia,  from  south- 
west to  north-east.  These  low  mean 
'  pressures  are  by  no  means  constant  in  all 
cases  during  the  months  of  the  year.  In 
the  Antartic  Ocean  they  are  nearly  con- 
stant during  the  months,  with  perhaps  a 
slight  tendency  to  an  increase  in  winter. 


24 


In  the  region  of  low  pressure  around  Ice- 
land the  pressure  is  a  little  less  than 
elsewhere  in  summer;  but  in  winter, 
when  the  rainfall  is  heaviest,  it  is  very 
much  less,  being  0.251  inch  less  in  winter 
than  in  summer  at  Reykjavik,  and  0.189 
at  Sandwich,  in  Orkney.  Similarly  at 
Petropaulovski,  in  Kamtschatka,  the 
pressure  in  winter  is  0.323  less  than  in 
summer.  Hence  the  low  mean  annual 
pressures  in  the  North  Atlantic  and  the 
North  Pacific  are  chiefly  brought  about 
by  the  low  pressure  during  the  cold 
months  of  the  year,  and  are  doubtless 
caused  by  the  copious  rainfall  during  that 
season.  On  the  other  hand,  in  Southern 
Asia,  the  lowest  pressures  occur  in  sum- 
mer. Thus,  at  Calcutta  it  is  29.408  in 
July,  while  in  January  it  is  30.102 — the 
average  pressure  for  that  degree  of  north 
latitude.  Hence,  in  Hindostan,  the  low 
mean  annual  pressure  arises  from  the 
very  low  pressure  in  summer  caused  by 
the  heavy  rains  falling  at  that  season, 
particularly  on  the  south  slope  of  the 
Himalayas.  Generally  the  pressure  is 


25 

low  wherever  a  copious  rainfall  prevails 
over  a  considerable  portion  of  the  earth's 
surface,  owing  to  the  large  quantity  of 
caloric  set  free  as  the  vapor  is  condensed 
into  rain. 

It  is  scarcely  necessary  to  point  out 
how  important  it  is  to  keep  in  mind  these 
facts  of  the  pressure  of  the  atmosphere, 
it  being  evident,  for  instance,  that  a  press- 
ure of  29.00  in  the  North  Atlantic  would 
portend  stormy  winds,  while  the  same 
pressure  south  of  Cape  Horn,  being  the 
mean  pressure  there,  would  indicate  set- 
tled weather. 

The  readings  of  the  mercurial  barome- 
ter are  subjected  in  nice  observations  to 
several  corrections : 

1st.  To  32°  F.  allowance  being  made 
for  expansion  of  both  mercury 
and  scale  for  all  observations 
above  that  temperature.  A  baro- 
metric pressure  of  thirty  inches 
at  32°  would  be  indicated  by  a 
height  of  30TV  inches  at  70°. 
2d.  For  decrease  of  gravitation  at  sta- 
tions above  the  level  of  the  sea, 


26 

acting  on  both  the  mercury  and 
the  air. 

3d.  For  increase  of  gravity  with  in- 
crease of  latitude. 

4th.  For  temperature  of  air ;  the  den- 
sity decreasing  as  temperature 
rises. 

5th.  For  humidity  of  the  air  which 
also  influences  its  density. 

6th.  For  capillary  attraction  of  the 
tube. 


27 


CHAPTEE  II. 

BAROMETRIC     MEASUREMENTS     OF     ALTITUDES. 

THE  text  books  in  physics  present 
formulas  for  computing  heights  from 
barometric  observations,  based  on  physi- 
cal laws  which  we  will  briefly  give. 

If  the  density  of  the  air  were  constant 
throughout,  the  measurement  of  heights 
would  be  a  problem  of  the  simplest 
character;  for  as  mercury  weighs  10,500 
times  as  much  as  air  at  the  sea  level,  the 
mercurial  column  would  fall  one  inch  for 
every  10,500  inches  of  ascent  above  the 
sea.  But  air  is  compressible,  and,  in 
accordance  with  Boyle's  law,  its  density 
varies  with  the  pressure  to  which  it  is 
subjected. 

Now  suppose  the  atmosphere  divided 
into  layers  of  uniform  thickness,  but  so 
thin  that  the  density  may  be  considered 
uniform  throughout. 


28 

Let  A=the  thickness  of  each  layer. 

W= weight  of  a  cubic  foot  of  air  at 

pressure  H. 

W, = weight  of  a  cubic  foot  of  air  at  H. , 
H0  H1?    &c.— pressures    measured    in' 

inches  of  mercury. 

Then  the  pressure  upon  the  unit  of 
surface  of  any  layer  is  greater  than  that 
upon  the  surface  of  next  higher  layer,  by 
the  weight  of  a  volume  of  air  whose  base 
is  the  unit  of  surface  and  whose  height 
is  the  thickness  of  the  layer.  If  one 
foot  be  the  unit  of  surface,  then  this 
quantity  would  be  AW.  And  to  express 
it  by  height  of  mercury  column,  it  is 

30 
necessary    to    multiply    by 


3  2157 

But  W  :  W0  :  :  H  :  30. 

W0  being  the  weight  of  a  cubic  foot  air 

at  the  level  of  the  sea  (=.0807  at  32°F). 

We  have  from  the  above  Wx  30= W0 

X  H,  and  the  above  expression  for  dimi- 

AW0H 

nution  may  be  written  . 


29 


If  H0  Ht  H2  represent  the  pressures 
at  the  surfaces  of  the  successive  layers, 
we  shall  have 

AWH 


AWH  /        AW 


H 


:n-Hn_t(i- 


21577 


Multiplying  these  equations  and  sup- 
pressing common  factors,  we  get 


H  _H     I 
Hn-H0  p_ 

If  A  be  taken  at  one  foot  then  n  would 
represent  the  number  of  feet  vertically 
between  two  stations  at  which  the  baro- 
metric pressures  are  Hn  and  H0  respect- 
ively. 

By  substituting  for  W0  its  value  and 
taking  logarithms  we  have 

H0          ,       /     2157 


whence 

n=60135.4xlog.=r9. 
i 

'X. 


30 

For  use  in  accurate  observations,  cor- 
rections are  required  for  temperature, 
humidity  and  variation  in  the  force  of 
gravity. 

La  Place's  formula  which  includes 
terms  derived  from  the  consideration  of 
these  conditions  is  obtained  as  follows  : 

Suppose  a  portion  of  the  atmosphere 
included  between  two  stations  at  differ- 
ent altitudes  to  be  divided  into  very  thin 
laminae. 

Let  z  be  the  distance  of  one  of  these 
from  the  surface  of  the  globe  and  dz  its 
thickness. 

Let  P  be  the  pressure  upon  a  unit  of 
surface  upon  the  lower  side  of  this  layer ; 
and  W  the  weight  per  cubic  meter  of  the 
air  at  this  pressure. 

Then  the  pressure  on  the  upper  side 
will  be  less  than  P  by  an  amount  equal 
to  the  weight  of  a  column  of  air  whose 
base  is  a  unit  and  height  is  equal  to  dz. 
Whence 

<£P=-W<fe (1) 

If  W0  be  the  weight  of  a  cubic  meter  of 
air  at  the  temperature  0°C  and  a  baro- 


31 

metric  pressure  of  O.m76,  the  weight  of 
this  same  volume  at  pressure  P  and  tem- 
perature 0  would  be 


°0.76' 

a  being  the  coefficient  of  dilatation  of 
air  which  is  here  taken  at  .004  in  conse- 
quence of  the  constant  presence  of  watery- 
vapor. 

This  expresses  the  weight  at  the  sur- 
face of  the  globe.  If  transferred  to  the 
height  2,  the  weight  would  be  diminished 
in  the  ratio  of  the  squares  of  the  distances 
from  the  center  of  the  earth.  We  should 
then  have 


_ 

°'0.76 

Substituting  in  equation  1,  dividing  by 
P  and  integrating  between  o  and  z,  we 
get,  by  calling  the  pressure  at  the  lower 
station  P 


_         _ 
5*  P~"0.76.  (l  +  «0) 

the  logarithm  being  Napierian. 
From  this  we  obtain 


32 

0.76 


But  the  pressures  P0  and  P  are  in  direct 
ratio  of  the  mercury  columns  which  we 
will  designate  by  h0  and  A.  These 
columns  also  vary  in  weight  in  accord- 
ance with  the  law  of  inverse  squares  of 
distance  from  the  earth's  center,  so  that 
P0  A0  (B  +  z)3 


P  ~  h         z2          h  V      B< 

Substituting  in  the  value  of  z,  we  have 
_0.76.(l  +  q0) 

Twr 


But  as  z  is  so  very  small  compared  with 
B1  we  may  replace   log.  f  1  +  —  J  by  —  . 

Also    r—  -  may  be  neglected. 

ii 

We  shall  then  have 
0.76(1  +  ^(9) 


The  weight  W0  refers  to  the  height  /^ 
the  lower  of  the  two  stations.     At  the 


33 

surface  of  the   earth,  this  weight  would 

/•p\2 

be  greater  in  the  ratio  of  ._;    '..a 

(^K  —  /I)  .       ±>Ut 

as  h  is  always   small   compared  with  H 
this  correction  may  be  neglected. 

But  there  is  another  of  more  import- 
ance which  should  be  taken  into  account. 
On  account  of  the  spheroidal  form  of 
the  globe  weight  varies  with  the  lati- 
tude. If  G  represent  the  weight  of  a 
body  at  latitude  45°,  then  at  any  other 
latitude  Z,  its  weight,  is  found  by  multi- 
plying G  by 

1-.  00265  cos.  2  I 

This  factor  is  to  be  applied  to  W0  in 
the  formula.  This  is  accomplished  by 
multiplying  the  above  value  of  z  by 
1  +  00265  cos.  2  I. 

In  order  to  simplify  the  expression  we 
will  substitute  for  6  the  mean  between  the 
temperatures  of  the  upper  and  lower 
stations,  designated  by  tQ  and  t.  The 
factor  1  +  aO  then  becomes 

since  «=.004; 


and  the  value  of  z  may  be  written 


34 


(1  +  . 00265  cos.  2  I) 

If  M  be  used  to  represent  the  modulus 
of    the   Napierian    logarithms    we   may 
write 
0.76 

2  = 


MW  I  1000     ) 

A°     2Mz  ] 


(1  +  0.00265  cos.  21) 

in  which  the  logarithms  are  of  the  com- 
mon kind. 

This  is  La  Place's  formula,  h  in  the 
expression  is  not  the  barometric  height 
directly  observed  at  the  upper  station, 
but  this  height  reduced  to  the  tempera- 
ture of  the  lower  station. 

0  7fi 

The  value  of  MW  has  been  determ- 
ined by  trial  of  the  formula  upon  known 
altitudes.  Kamond  in  his  survey  of  the 
Pyrenees  determined  its  value  to  be 
18336. 


35 


The  unknown  term  z  in  the  second 
member  is  determined  by  successive  ap- 
proximations. 

The  first  value  being 

*/  =  18336.  log.  j-  (meters) 
This  being  substituted,  we  may  have 

-_-      2(*.  +  Os    * 

2     ^        1000      l' 

Finally,  these  being  substituted  in  the 
above  value  of  z  we  get 

.,=1888610**-+^ 

4-4t.00966.oo8.lI 

+  (za  +  2M.  18336)^ 

The  terms  of  this  formula  are  gener- 
ally reduced  to  tabular  form  for  practi- 
cal use. 

Guyot's  formula  which  is  derived  from 
this,  reducing  meters  to  feet  and  the  con- 
stants depending  on  temperature  being 
changed  to  accord  with  Fahrenheit's 
scale,  is 

2=60158.6  log.  - 


36 


900 

(1  +  .00260  cos.  21) 
/        z  +  52252 

I        ' 


20886860^104434307 
The  three  terms  after  the  first  are  the 
corrections.  The  first  being  that  for  the 
temperature  at  the  two  stations.  The 
second  is  the  correction  for  the  force  of 
gravity  depending  on  the  latitude. 

The  third  contains,  first  the  correction 
for  action  of  gravity  on  the  mercury 
column  at  the  elevation  z,  and  second  a 
correction  required  for  decrease  in  densi- 
ty of  air  owing  to  decrease  in  action  of 
gravity  at  the  greater  elevation.  The 
factor  s  being  the  approximate  difference 
in  altitude  of  the  stations. 

Plantamour's  formula,  which  has  been 
much  used,  differs  slightly  from  Guyot's. 
The  first  coefficient  is  60384.3.  The  de- 
nominator of  temperature  term  is  982.26 
and  a  separate  correction  is  used  for 
humidity  of  the  air. 

To  use  either  of  these  formulas  tables 
are  necessary,  of  which  those  prepared 


37 


by  Lieut.  Col.  Williamson*  are  the  most ' 
elaborate. 

For  the  Aneroid  in  ordinary  practice, 
formulas  of  much  less  complexity  may 
be  profitably  used.  The  corrections  de- 
pending upon  the  gravity  of  the  mercury 
column  would,  in  any  case,  be  omitted. 
The  other  corrections  may  in  very  nice 
work  be  retained.  But  a  correction  de- 
pending on  the  effect  of  changes  of  tem- 
perature on  the  metallic  work  of  the 
instrument ,  should  be  carefully  remem- 
bered. First-class  Aneroids  claim  to  be 
compensated,  but  a  greater  portion  will 
need  a  correction  which  the  purchaser 
can  determine  for  himself,  by  subjecting 
the  instrument  to  different  temperatures 
while  the  pressure  remains  constant. 

A  modification  of  Guyot's  formula 
adapted  to  aneroid  work  was  suggested 
in  an  excellent  paper  on  the  use  of 
the  aneroid,  read  before  the  American 
Society  of  Civil  Engineers,  in  January, 
1871 

*  The  use  of  the  Barometer  on  Surveys  and  Recon- 
noisances.  By  R.  S.  Williamson.  New  York  :  D.  Van 
Nostrand.  London  :  Trubner  &  Co. 


38 

It  is 
D=60000  (logH-log/o(l+ 

D  is  the  difference  of  altitude  in  feet. 
H  and  A  are  the  barometric  readings  in 
inches. 

T  and  t  are  the  temperatures  of  the 
air  at  the  two  stations. 

Table  II  is  prepared  for  the  use  of 
this  formula. 

Other  formulas  will  be  given  in  another 
chapter. 


39 


CHAPTER  III. 

ANEROID  BAROMETERS:    THEIR  CONSTRUCTION. 

THE  general  principle  of  construction 
of  all  aneroids  is  the  same.  A  box  with 
flexible  sides,  hermetically  sealed,  the  air 
having  been  first  exhausted,  changes  its 
form  as  the  pressure  of  the  atmosphere 
varies. 

The  chief  differences  in  the  various 
kinds  lie  in  the  mechanical  devices,  by 
which  the  motions  of  the  box  are  ren- 
dered apparent  to  the  eye,  and  also  meas- 
sured  in  such  a  manner  as  to  allow  the 
corresponding  pressures  to  be  expressed 
in  inches  of  mercury. 

The  aneroid  was  invented  about  the 
beginning  of  this  century,  but  was  first 
made  of  a  serviceable  form  by  Vidi,  in 
1848.  It  is  substantially  the  form  most 
used  to-day.  The  vacuum  box  is  a  thin 
low  cylinder,  and  the  motion  of  the  thin 
flexible  head  of  the  cylinder  is  conveyed 


40 


by  suitable  mechanism  to  the  index 
hand.  Vidi's  aneroid  is  shown  in  Fig.  1. 
D  is  the  vacuum  box,  supporting  the  up- 


right pillar  M  upon  its  center.  As  M; 
rises  or  falls,  a  corresponding  motion  is 
given  to  the  plate  C.  A  counter  pressure 


41 


is  afforded  by  the  spiral  spring  S.  The 
motion  of  C  is  conveyed  by  the  links  1 
and  2  to  a  little  rocker  shaft,  shown  in 
the  figure.  An  arm,  3,  attached  to  this 


shaft  is  connected  by  a  minute  chain 
with  the  shaft  which  carries  the  index 
pointer.  It  is  kept  wound  to  the  proper 
tension  about  this  shaft  by  a  fine  spiral 
hair  spring. 


42 

A   modification   of    this   is    shown   in 
Figs.  2  and  3.     (See,  also,  frontispiece). 


Fig,3 


This  is  Naudet's  aneroid,  and  is  the  one 
chiefly  employed  now.  It  differs  from 
Vidi's  in  the  substitution  of  the  thin 


43 

laminated  spring  (B  in  frontispiece)  for 
the  spiral  spring  (S  in  Fig.  1). 

One  of  the  oldest  forms  of  box  barom- 
eter  and    the    one  to  which    the  name 


Fig.  4. 

aneroid  is  restricted  by  some  writers,  is 
represented  in  Fig.  4.  A  rectangular 
tube,  from  which  the  air  has  been  per 
fectly  exhausted,  is  sealed  hermetically, 


44 

and,  having  been  bent  into  the  form  rep- 
resented in  the  figure  by  cbd,  is  made 
fast  at  the  middle  point  b.  The  varying 
pressure  of  the  atmosphere  causes  the 
extremities  c  and  d  to  approach  or  recede 
from  each  other.  This  motion  is  con- 
verted into  a  to-and-fro  traverse  of  the 
index,  by  a  mechanism  sufficiently  well 
exhibited  by  the  diagram.  c 

This  is  known  as  Bourdon's  form.  It 
is  not  now  employed  for  delicate  work. 
The  forms  of  Vidi  and  Naudet  are,  by 
some  writers,  designated  the  holosteric 
barometers. 

The  graduation  of  these  instruments 
is  made  to  correspond  with  the  height  of 
the  mercurial  barometer,  and  is  expressed 
as  inches  or  millimeters. 

The  difficulties  to  be  met  by  the  maker, 
in  securing  accuracy  of  working,  are  those 
which  arise  chiefly  from  the  varying  elas- 
ticity of  the  several  metallic  elements 
under  change  of  temperature.  Greater 
simplicity  of  construction  might  be  pre- 
sumed to  be  attended  with  a  smaller  lia- 
bility to  a  kind  of  error,  for  which  it  it 


45 


exceedingly  difficult  to  compensate.  This 
is  the  theory  of  the  Goldschmid  Aneroid. 

The  instrument  designed  for  ordinary 
engineering  use  is  represented  by  Fig.  5. 
The  size  recommended  by  the  present 
makers  for  this  service  is  3J  inches  in 
diameter  and  2J-  inches  high. 

The  construction  is  exhibited  by  Fig. 
6.  The  vacuum  box,  constructed  as  be- 
fore described,  is  shown  at  aa.  The  mo- 
tions of  the  box,  caused  by  variations  of 
atmospheric  pressure,  are  conveyed  di- 
rectly to  the  lever,  whose  fulcrum  is  at 
e",  and  whose  free  end  is  at  e.  This  end, 
projecting  through  the  side  of  the  cas- 
ing and  working  freely  through  a  slot,  is 
observed  with  a  magnifying  lens,  and  the 
reading  on  the  index  ff  taken.  But  it  is 
evident  that  the  lever,  working  with 
proper  ease  on  its  fulcrum,  must  be  sup- 
plied with  a  certain  amount  of  counter- 
pressure.  This  is  ingeniously  done  by 
aid  of  the  delicate  spring  e',  which  is  at- 
tached to  the  lever  near  the  fulcrum. 
Bearing  on  the  spring  is  the  point  of  the 
micrometer  screw  M,  whose  head  is  grad- 


46 


uated  to  hundredths  and  forms  the  top 


of  the  case.     Both  lever  and  spring  are 
furnished  at  their  extremities  with  bright 


47 

metal  heads,  whose  end  surfaces  lie  in 
the  same  plane.  The  head  e'  is,  under 
ordinary  conditions,  higher  than  e,  as 
shown  in  Fig.  6.  When  a  reading  is  to 
be  taken  the  top  of  the  case  is  turned 
until  e'  and  e  are  side  by  side  ;  the  hori- 
zontal marks  borne  on  the  metallic  heads 
being  brought  to  an  exact  coincidence  by 
aid  of  a  lens  (P  in  Fig.  5).  The  reading 
of  the  Inches  is  taken  from  the  scale  ff^ 
and  of  the  hundredths  from  the  divisions 
on  the  scale  around  the  top  of  the  box 
T ;  a  fixed  point  c  being  marked  on  the 
cylinder.  In  figure  7  the  indices  exhibit 
a  reading  of  29.75  inches. 

The  thermometer  F  is  an  important 
part  of  the  instrument. 

In  some  of  these  instruments  the  scale 
ff  bears  no  reference  to  the  inches  of  the 
mercurial  barometer,  but  is  of  an  arbi- 
trary character,  and  is  different  for  dif- 
ferent instruments.  The  value  of  the 
divisions  is  determined  by  comparison 
with  standard  instruments,  and  is  care- 
fully expressed  in  tabular  form  on  the 
cover  of  the  box 


48 


Some  corrections  for  temperature  and 
pressure  are  required  in  the  use  of  these 
instruments  which,  although  desirable  in 
the  more  common  forms  of  aneroid,  have 
not  heretofore  been  considered  necessary. 
In  the  latter  instruments,  however,  when 
of  the  best  construction,  a  compensation 
has  been  effected  which  renders  a  correc- 
tion for  temperature  unnecessary.  In 
the  Goldschmid  aneroids  no  compensa- 
tion is  attempted,  but  each  instrument  is 
furnished  with  a  table^  of  corrections 
which  have  been  prepared  from  observa- 
tion on  standard  instruments. 

Thus,  aneroid  No.  3187,  imported 
last  year,  bears  on  the  cover  the  follow- 
ing: 

CORRECTION  TABLE. 

For  Division.  For  Temperature. 

26.0"= -0.02  28°  to  48°=     0 

26.5"  =  -0.03  52°=:  +0.01 

27.0"=-0.03  56°= +0.015 

27.5  =-0.02  60°= +0.025 

28.0  =     0  64°= +0.035 

28.5  =  +0.03  68°= +0.04 

29.0  =  +0.06  72°= +0.05 


49 

For  Division.        For  Temperature. 
29.5"=: +0.10  76°= +0.07 

30.0  =  +  0.14  80  =+0.09 

30.5  =+0.19  84  =+0.11 

31.0  =+0.25  88  =+0.13 

92°= +0.15 

The  temperatures  are,  of  course,  taken 
from  the  thermometer  that  forms  a  part 
of  the  instrument,  and  which,  when  the 
latter  is  carried  slung  from  the  shoulder, 
may  exhibit  a  temperature  considerably 
higher  than  that  of  the  air. 

A  smaller  and  ruder  instrument  called 
the  Pocket  Aneroid  is  made  by  the 
Zurich  manufacturers.  It  is  only  1J 
inches  in  diameter  and  1^  inches  high. 
A  bar  fastened  to  the  top  of  the  vacuum 
box  takes  the  place  of  the  lever  in  the 
larger  instrument. 

A  larger  size  is  also  made  in  which  the 
movements  of  the  vacuum  box  are  di- 
rectly observed  with  a  compound  micro- 
scope. 

There  is  no  doubt  that  all  aneroids 
need  a  careful  comparison  with  standard 
instruments  or  a  series  of  trials  upon 


50 

known  altitudes,  in  order  to  determine 
the     proper     corrections.       Such    trials 


.>  o 


should  be  made  at  different  temperatures 
and  under  different  conditions  as  to  ris- 
ing or  falling  at  the  time  of  observation. 


51 

The  tables  of  corrections  furnished  by 
the  maker  cannot  well  be  substituted  for 
those  made  by  a  careful  observer  deduced 
from  systematic  work.  The  air  pump, 
the  hot  chamber  and  the  freezing  box 
are  convenient,  but  inadequate  substi- 
tutes for  a  large  number  of  trials  under 
normal  conditions. 


52 


CHAPTEK  IV. 

THE  USE  OF  ANEROID  BAROMETERS. 

The  Aneroid,  like  the  Mercurial  bar- 
ometer may  be  used  either  as  a  weather 
indicator  or  in  the  measurement  of  alti- 
tudes. When  used  in  the  former  capa- 
city, the  Aneroid,  especially  at  sea,  pos- 
sesses some  obvious  advantages.  Aside 
from  its  superior  compactness  of  form 
and  its  portability,  it  responds  more 
readily  to  the  changes  in  atmospheric 
pressure  than  the  Mercury  column,  and 
thereby  serves  more  efficiently  to  warn 
the  mariner  of  sudden  tempests. 

The  words  Rain — Change — Fair  seen 
stamped  or  engraved  on  the  dial  of  many 
barometers  have,  of  course,  no  special 
significance,  and  are  now  rarely  seen  on 
first-class  instruments  of  either  kind.  The 
probable  changes  of  weather  indicated  by 
changes  of  the  barometer  are  briefly  set 
f crth  in  the  following : 


53 


KULES  FOE  FORETELLING  THE  WEATHER. 

A  Rising  Barometer. 

A  "  rapid  "  rise  indicates  unsettled 
weather. 

A  "  gradual  "  rise  indicates  settled 
weather. 

A  "  rise "  with  dry  air,  and  cold  in- 
creasing in  summer,  indicates  wind  from 
Northward ;  and  if  rain  has  fallen  better 
weather  is  to  be  expected. 

A  "rise"  with  moist  air,  and  a  low 
temperature,  indicates  wind  and  rain 
from  Northward. 

A  "  rise "  with  southerly  wind  indi- 
cates fine  weather. 

A  Steady  Barometer. 

With  dry  air  and  seasonable  tempera- 
ture, indicates  a  continuance  of  very  fine 
weather. 

A  Falling  Barometer. 

A  "rapid"  fall  indicates  stormy 
weather. 

A  "rapid"  fall,  with  westerly  wind, 
indicates  stormy  weather  from  North- 
ward. 


54 

A  "  fall,"  with  a  northerly  wind,  indi- 
cates storm,  with  rain  and  hail  in  sum- 
mer, and  snow  in  winter. % 

A  "  fall,"  with  increased  moisture  in 
the  air,  and  the  heat  increasing,  indicates 
wind  and  rain  from  Southward. 

A  "  fall  "  with  dry  air  and  cold  increas- 
ing (in  winter)  indicates  snow. 

A  "fall"  after  very  calm  and  warm 
weather  indicates  rain  with  squally 
weather. 

It  does  not  require  the  highest  quality 
in  the  mechanism  of  an  Aneroid  to  serve 
the  purpose  indicated  in  the  ab^ove 
rules. 

For  the  accurate  measurement  of  dif- 
ferences of  altitude,  however,  the  best 
skill  in  construction  and  the  most  care- 
ful adjustment  of  the  parts  is  indispens- 
ably necessary.  The  use  of  an  Aneroid 
of  even  medium  quality  will  frequently 
lead  to  considerable  errors  in  estimating 
heights.  It  may  also  be  added  here  that 
instruments  of  the  best  manufacture  in 
the  hands  of  observers  unacquainted  with 
the  principles  involved,  will  often  lead  to 


55 

erroneous  conclusions.  This  is  owing  in 
many  cases  to  a  method  adopted  by  some 
makers  of  adding  a  circle  marked  feet 
outside  of  the  common  graduation  to 
inches  of  mercury. 

Many  tourists  carry  Aneroids  of  the 
pocket  size,  and  consult  them  frequently 
while  traveling,  relying  upon  a  single 
observation  of  the  index  for  the  deter- 
mination of  their  altitude. 

If  such  a  circle  of  feet  be  engraved  on 
the  dial  plate  with  the  zero  mark  made  to 
correspond  with  30  inches  of  the  mercury 
column,  of  course  every  estimate  of  alti- 
tude made  as  above  mentioned  assumes 
that  at  the  moment  of  observation  ;  the 
barometer  at  the  level  of  the  sea  would 
stand  exactly  at  30  inches  ;  a  condition 
only  realized  occasionally.  And  the  fur- 
ther condition  is  also  assumed,  that  the 
temperature  of  the  air  is  of  no  account 
in  estimating  heights;  an  assumption 
equally  at  variance  with  fact. 

It  is  only  an  inferior  class  of  Aneroids 
that  bear  a  fixed  graduated  circle  of  feet, 
with  the  zero  of  altitude  corresponding 
to  30  inches  of  pressure. 


56 


Prof.  Airy,  the  former  Astronomer  Royal 
of  Great  Britain,  prepared  a  table  for  the 
use  of  barometer  makers — a  scale  from 
which  is  now  engraved  on  many  English 
Aneroids.  It  places  the  zero  of  altitude 
at  31  inches  of  pressure.  This  affords 
such  large  numbers  for  slight  elevations 
that  the  proper  use  of  the  rule  is  sug- 
gested to  the  observer.  He  is  led  to 
subtract  the  two  readings  of  feet  to  get 
difference  in  height.  But  this  again  as- 
sumes that  the  average  temperature  is 
50°  F. 

Table  I  exhibits  Prof.  Airy's  series  of 
heights. 

Some  makers,  designing  to  improve 
upon  the  simple  construction  just  de- 
scribed, have  engraved  the  outer  circle 
of  feet  on  a  movable  ring  encircling  the 
dial,  so  that  when  an  observer  is  at  any 
locality  whose  height  is  known,  he  may 
bring  the  proper  mark  of  the  altitude 
scale  against  the  index  pointer.  Then  if 
the  observer  travels  about  over  a  section 
of  country,  the  pointer  will  indicate  with 
fair  approximation  for  some  hours  the 
altitude  of  the  new  positions. 


FIELD'S  ENGINEERING  ANEROID. 

(For  description,  see  page  57.) 


57 


This  device  is  convenient  to  a  skilled 
observer  who  only  requires  rapid  and 
approximate  results,  but  to  the  novice  it 
is  misleading  in  two  ways  ;  first,  because 
the  temperature  is  left  out  of  the  calcula- 
tion, and  furthermore,  such  a  use  of  the 
movable  scale  will,  at  times,  involve  a 
large  error,  as  it  is  not  a  scale  of  equal 
parts. 

Mr.  Eogers  Field,  C.  E.,  in  1873,  ap- 
plied the  movable  scale  to  the  Aneroid,  so 
as  to  convert  it  from  a  source  of  inaccu- 
racy into  an  aid  towards  accuracy.  He 
employs  the  altitude  scale  proposed  by 
Sir  G.  Airy  for  temperature  50°,  but  he 
makes  it  movable  so  as  to  adjust  it  for 
any  other  temperature.  The  shifting  of 
the  scale  into  certain  fixed  positions,  is 
made  to  answer  the  same  purpose  as  if 
the  original  scale  were  altered  to  suit 
various  temperatures  of  the  air.  In  the 
Journal  of  the  Meteorological  Society  for 
1874,  January,  Mr.  Field  says : 

"  The  object  aimed  at  in  designing  this 
improved  form  of  Aneroid  was,  to  sim- 
plify the  correct  determination  of  alti- 


58 

tudes  in  cases  such  as  ordinarily  occur  in 
England,  and  the  instrument  is  therefore 
arranged  to  suit  moderate  elevations,  say 
of  2000  feet  and  under,  and  is  not  in- 
tended for  more  considerable  heights. 

"  The  Aneroid  is  graduated  for  inches 
in  the  usual  way  on  the  face,  but  the 
graduation  only  extends  from  31  inches 
to  27  inches  so  as  to  preserve  an  open 
scale.  The  outer  movable  scale  is  grad- 
uated in  feet  for  altitudes,  and  this  grad- 
uation is  laid  down  by  fixing  the  movable 
scale  with  the  zero  opposite  31  inches. 
This  is  the  normal  position  of  the  scale 
and  it  is  then  correct  for  a  temperature 
of  50°.  For  temperatures  below  50°  the 
zero  of  the  scale  is  moved  below  31  inches; 
for  temperatures  above  50°,  the  zero  of 
the  scale  is  moved  above  31  inches.  The 
exact  position  of  the  scale  for  different 
temperatures  has  been  determined  partly 
by  calculation  and  partly  by  trial,  and 
marked  by  figures  engraved  on  the  out- 
side of  the  Aneroid.  In  order  to  insure 
the  altitude  scale  not  being  shifted,  after 
it  has  once  been  set  in  its  proper  position 


59 


there  is  a  simple  contrivance  for  locking 
it  in  the  various  positions.  This  consists 
of  a  pin,  which  fits  into  a  series  of  notch- 
es on  the  outside  of  the  ring  carrying  the 
glass.  By  slightly  raising  the  glass  it  is 
freed  from  this  locking  pin,  and  can  be 
turned  until  the  figures  corresponding  to 
the  air  temperature  are  opposite  to  the 
pin,  when  the  glass  should  be  depressed 
so  as  to  relock  it,  and  the  scale  becomes 
correct  for  that  temperature.  The  alti- 
tudes are  in  all  cases  determined  by  tak- 
ing two  readings,  one  at  each  station, 
and  then  subtracting  the  reading  at  the 
lower  station  from  that  at  the  upper. 

"  It  will  be  seen  from  the  foregoing 
description  that  the  movable  sdale  of  the 
instrument  requires  to  be  set  for  tem- 
peratures before  taking  any  observations, 
and  must  not  be  shifted  during  the  prog- 
ress of  the  observations. 

"  This  may  appear  at  first  sight  as  a 
defect,  inasmuch  as  the  temperature  of 
the  air  may  alter  during  the  progress  of 
the  observations ;  but  practically  it  will 
not  be  found  to  be  any  drawback  in  the 


60 

case  of  moderate  altitudes,  as  small  vari- 
ations of  temperature  will  not  appreciably 
affect  the  result.  A  variation  of  5°  of 
temperature  gives  only  about  1  per  cent, 
variation  in  the  altitude,  an  amount  that 
would  under  ordinary  circumstances  be 
inappreciable,  so  that  as  long  as  the  tem- 
perature does  not  vary  during  the  course 
of  the  observations  more  than  5°  from 
that  at  which  the  instrument  is  set,  the 
results  may  be  accepted  as  correct,  and, 
generally  speaking,  even  a  greater  varia- 
tion than  this,  say  6°  or  8°,  would  be 
practically  of  no  importance.  Of  course, 
if  it  should  be  found  at  any  time  that 
the  temperature  has  varied  considerably, 
during  the  course  of  the  observations, 
from  that  at  which  the  instrument  was 
set,  this  variation  can  be  allowed  for  by 
calculation  in  the  usual  way." 

The  principle  of  allowing  for  variation 
of  temperatures  of  the  air  by  shifting  the 
altitude  scale  is  not  theoretically  accurate, 
but  sufficiently  so  for  practical  purposes. 
For  altitudes  within  the  range  of  the  in- 
strument (say  3000  feet  and  under)  and 


61 

temperatures  between  30°  and  70°,  the 
maximum  error  from  usin~  the  shifted 
scale,  instead  of  the  calculation,  is  only 
2  feet,  which  is  inappreciable  on  the 
scale.  The  same  principle  might  even 
be  applied  to  altitudes  up  to  6000  feet, 
as  the  maximum  error  would  be  only  10 
feet.  For  considerable  elevations,  how- 
ever, the  variations  of  the  temperature 
between  the  base  and  the  summit  would 
interfere  with  the  application  of  the  prin- 
ciple. 

Nevertheless,  the  best  plan  is  to  dis- 
pense with  altitude  scales,  whether  fixed 
or  movable,  and  to  calculate  the  heights. 
Simple  rules,  giving  more  reliable  results 
than  the  attached  scales,  are  at  the  ser- 
vice of  those  who  need  easy  processes. 
Among  these  are  the  following : 

Note  the  rise  or  fall  of  the  barometer 
in  hundredths  of  an  inch,  in  passing 
from  one  station  to  the  other  •  multiply 
by  9.  The  product  is  the  difference  of 
altitude  in  feet. 

This  is  for  ordinary  temperatures  and 
pressures.  If  the  pressure  is  below  26 


62 


inches  or  the  temperature  above  70°,  use 
10  for  a  multiplier. 

A  higher  degree  of  accuracy  is  obtained 
by  using  the  multiplier  obtained  from  the 
following  table  prepared  by  Mr.  G.  J. 
Symons : 


Mean  temperature.  .  . 

30° 

40° 

50° 

60° 

70° 

80° 

Mean  presssure,  27in. 
28in. 

9.7 
9.8 

9.910.1 
9.5   9.8 

10.3 
10.0 

10.6 
10.2 

10.8 
10.4 

29in. 

9.09.2   9.4 

9.6 

9.8 

10.0 

30in. 

8.78.9 

9.1 

9.3 

9.5 

9.7 

To  find  the  difference  in  height  be- 
tween two  stations :  Find  the  mean 
pressure;  also  the  mean  temperature. 
The  number  in  the  table  corresponding 
to  these  two  means,  if  multiplied  by  the 
difference  of  the  barometric  pressures  in 
hundredths  of  an  inch^  mil  give  the  dif- 
ference in  altitude  very  nearly. 

In  the  absence  of  a  table  to  aid  in 
computation,  but  having  an  Aneroid  with 
the  scale  of  feet,  use  the  formula, 


D=55000; 


H-A 
H+X 


63 


adding  -%^  of  the  estimated  altitude  for 
every  degree,  the  average  temperature  is 
above  55°,  and  subtracting  a  like  amount 
when  it  is  below.  D,  is  the  difference  of 
altitude  in  feet;  H  and  h  are  the  read- 
ings in  feet  from  the  Aneroid  scale.  This 
gives  fair  approximations  up  to  3000 
feet. 

For  accurate  results  use  one  of  the 
following  methods  :  Having  Airy's  table 
(Table  1)  and  an  Aneroid  carefully  grad- 
uated to  inches  ;  Take  the  reading  in 
inches  of  the  baromteric  scale  at  both 
lower  and  upper  stations  ;  also  the  tem- 
perature at  both  stations.  Find  from 
the  table  the  heights  in  feet  correspond- 
ing to  the  barometer  readings.  Subtract 
them  and  multiply  the  remainder  by 

\ 


1000 

The  complete  formula  is 


T  and  t  are  the  observed  temperatures  ; 
H  and  h  are  the  heights  in  feet  taken 
from  the  table. 


64 

In  the  absence  of  this  table,  but  with 
a  table  of  logarithms  at  hand,  the  baro- 
metric heights  in  inches  are  to  be  taken, 
and  the  following  formula  used  : 

D=60000  (log.  B-log.  b) 


900 

B  and  b  are  the  barometric  readings  in 
inches  ;  D,  T  and  t  as  in  the  other  for- 
mulas. (See  Table  II.) 

To  avoid  error  from  the  constant 
changes  in  barometric  pressure,  the  ob- 
servations should  be  simultaneous.  This 
is  accomplished  in  the  best  manner  by 
using  two  instruments,  and  requires, 
when  the  distance  between  the  stations 
is  considerable,  two  observers.  With 
one  instrument  only,  large  errors  are 
avoided  by  repeating  the  observation  at 
the  first  station  after  taking  that  at  the 
2d  station,  and  assuming  that  any  change 
in  barometric  pressure  that  has  occurred 
has  been  gradual  during  the  absence. 

When  it  is  impracticable  to  repeat  the 
observation  at  the  first  station,  the  error 


65 


which,  in  case  of  a  changing  pressure, 
might  be  a  large  one,  may  be  reduced  if 
the  observation  at  the  2d  station  be  con- 
tinued for  an  hour  or  two,  or  until  the 
rate  of  change  can  be  estimated  and  a 
proportionate  correction  applied. 

Many  Aneroids  marked  "compensated" 
exhibit  a  sensible  change  when  the  tem- 
perature is  varied ;  such  instruments  may 
be  serviceable  and  quite  accurate  if 
allowance  be  made  for  the  error  of  the 
instrument.  This  correction  the  owner 
had  better  determine  by  experiment.  It 
is  easy  to  subject  the  Aneroid  to  such 
variation  of  temperature  as  shall  embrace 
the  range  at  which  it  is  likely  to  be  used, 
and  the  movement  of  the  index  for  each 
10°  or  20°  of  temperature  recorded. 

Aneroids  require  to  be  compared  from 
time  to  time  with  a  good  mercurial  baro- 
meter. While  making  such  comparisons, 
it  is  well  to  remember  that  the  mercurial 
column  and  the  scale  by  which  it  is 
measured  both  require  correcting,  and 
that  during  times  of  rapid  changes,  in 
atmospheric  pressure,  the  Aneroid  shows 


66 

such  changes  more  readily  than  the 
mercurial  barometer.  (See  Table  IV.) 

In  measuring  heights  with  the  Aner- 
oid care  should  be  taken  that  the  instru- 
ment is  not  influenced  by  the  heat  of  the 
hand  nor  by  the  direct  rays  from  the 
sun. 

The  instrument  should  always  be  tap- 
ped gently  with  the  finger  at  the  moment 
of  taking  an  observation.  It  should 
also  be  held  in  the  same  position  for 
both  observations ;  preferably  with  the 
face  horizontal. 

Considerable  care  is  also  required  to 
determine  exactly  where  the  index 
points.  It  is  best  accomplished  by  sight- 
ing along  the  pointer,  using  one  eye  only 
for  the  purpose. 

The  following  example  will  illustrate 
the  use  of  the  tables. 

Barometer  at  Station  A  30. 04  Thermometer  78° 
B  28.68  "  65° 

From  Table  I  we  find  height  corre- 
sponding to  reading  at  A  is  857  feet. 
The  height  for  B  is  2120  feet. 

The  approximate  height  is  2120—857 


67 


=  1263  feet  ;  but  the  sum  of  the  tempera- 
tures is  143°.  An  additional  correction 
of  Tff  -g-  is,  therefore,  to  be  applied  to  the 
above  difference;  this  is  54  feet.  The 
total  estimated  difference  of  altitude  is 
then  1263  +  54=1317  feet. 

The  formula  directly  applied  is 


=  1317.21 

Applying  the  logarithmic  formula  we 
have: 

Log.  B  30.  04=  1.477700 
"     b  28.68  =  1.457579 


Log.  B— Log.  5=0.020121 

78  +  65-60\ 


( 
1 


900        / 

feet. 

As  before  remarked,  the  Goldschmid 
Aneroid  requires  that  both  the  tempera- 
ture of  the  air  and  of  the  instrument  be 
carefully  taken.  Two  examples  of  alti- 
tudes taken  with  the  instrument  prev- 
iously referred  to  (No.  3187)  will  serve 
to  show  the  kind,  of  correction  necessary, 


68 

and  as  both  examples  apply  to  the  same 
mountain  (Kiarsarge  of  Conway,  N.  H.,) 
they  will  together  indicate  the  character 
of  the  instrument. 

Ex.  I. — JFLY  9-TH,  1881. 


Station. 


^  Temp.  Correct   :>    ^  •_ 


Time. 


c. 

—       = 

-       ."- 


^ir.  6. 00  AM.  29.51  66   66    -.04  ^.1029.65 
Mt.  Kiar- 
sarge.. l.OOp.M  26.75  74   74   +.06  -.0: 


Ex.  II. — AUGUST  9xH,  1881. 

bi  Temp.  Corm-:':->    ^  ^ 
Station.      Time.     J^>:_       f        S       £  ^ 

FrveVg.  7.00A.M.  29.3460   65    -.03  -.09  39.46 
Mt' Kiar- 
sarge. 1.20P.M.  26.4S65"  75'  4--06— .03  26.51 


In  both  these  examples  another  read- 
ing would  have  been  taken  at  Erveburi: 
on  the  return,  if  the  better  alternate 


69 


securing  hourly  readings  of  a  stationary 
barometer  at  Fryeburg  had  not  been  fol- 
lowed. On  July  9th  there  was  no  change 
in  the  Fryeburg  barometer.  On  August 
9th  the  following  readings  were  taken  at 
Fryeburg: 


7  A.  M.  29.53 

1  P.  M. 

29.40 

8  "   29.52 

2  •• 

29.455 

10  u   29.515 

3  u 

2940 

12  "   29.46 

As  this  set  of  observations  indicates  a 
fell  of  .07  in  the  interval  between  the 
base  and  summit  readings,  it  becomes 
necessary  to  make  another  correction  to 
the  last  column. 

Correcting  the  first  reading  to  accord 
with  the  fall  indicated  by  the  stationary 
barometer,  we  get  after  all  corrections: 

Fryeburg,  29.39. 
Mt.  Kia:  -'"'.51. 

The  logarithmic  formula  for  estimating 
heights  from  barometric  observations  is 

/         T  —  f 60  \ 

D=60000(log. B-log.  - .   ( 1  -  '         —  ) 

in  which 


70 

D  =  difference  in  altitude  in  feet. 

B=  height  of  barometer  in  inches  at 
lower  station. 

b  =  height  of  barometer  in  inches  at 
upper  station. 

T  and  t  are  the  temperatures  of  the  air 
in  Fahrenheit  degrees. 

Applying  this  formula  to  our  first  ex- 
ample we  have: 
D=60000(1.47202-  1.42781) 


The  second  example  gives  : 
D=60000(1.46820  -  1.42341) 


As  the  station  at  Fryeburg  is  434  feet 
above  the  sea,  the  estimated  total  height 
of  Kiarsarge  would  be,  in  one  case,  3321 
feet,  and  in  the  other  3315  feet. 

Prof.  Airy's  table  gives  3319  and  3314 
from  the  same  data. 

The  instrument  employed  in  the  above 
measurements  has  been  used  in  many 
other  cases  of  altitudes  from  3000  to 


71 


4000  feet.  An  error  of  about  2  per  cent, 
in  excess  has  been  detected  in  those  cases 
where  the  altitude  has  been  measured  by 
more  accurate  means.  It  seems  likely 
that  the  special  correction  table  needs 
some  slight  revision. 


The  following  measurement  was  made 
with  an  aneroid  only  1J  inches  diameter, 
made  by  Casella. 

Neversink,  Sullivan  Co.,  N.  Y.,  and 
Slide  Mountain,  Ulster  Co. 


Time. 

Bar. 
Readings 

T. 

Ht. 
Tab.  I. 

Neversink  

7  A.M. 

28  64 

6i° 

2158 

Fly  Club  Camp. 
Slide  Mountain. 

11    " 
4  P.M. 

27.92 
25.87 

78° 
69° 

2853 
4931 

=  (4931  -2158) 


61  +  69-100\ 


1000        / 
=  2773x1.03=2856  feet. 
As  Neversink  had  been   satisfactorily 
determined    to  be  1350  feet  above  the 
sea,    the  total   height  of   Slide  Mount- 
ain is  estimated  from  this    observation 
to  have  an  altitude  of  4206  feet. 


72 

(NOTE). — Beturn  observations  were 
made  only  at  the  camp  of  the  Fly  Club. 
Between  11  A.  M.  and  9  p.  M.,  no  change 
occurred  in  the  barometer. 

The  Tribune  report,  however,  indi- 
cates a  rise  on  this  date  of  .07  between 
7  and  11  A.  M.  If  such  a  change  was 
felt  in  this  region,  then  the  calculated 
height  of  the  mountain  is  too  low  by  at 
least  60  feet.  On  the  other  hand,  a 
height  given  by  railway  survey  in  this 
vicinity,  (Johnson's  Mill)  near  the  camp, 
seems  to  confirm  the  figures  given  here. 

Also,  the  height  of  Helsinger  Notch, 
taken  incidentally  on  this  excursion,  was 
estimated  at  2660  feet.  Guyot  makes 
the  Notch  2677  and  the  summit  of  Slide 
Mountain  4205  feet. 

The  height  of  the  base  at  Neversink 
was  established  by  four  observations, 
between  New  York  Bay  and  this  base, 
and  was  confirmed  by  comparison  with 
the  height  of  the  railway  track  at  Lib- 
erty, six  miles  southwest. 


73 


Neversink  to  Blue  Mountain,  August 

18,  1880. 


Time. 

Bar. 
Rd'g. 

T. 

Cor. 
Rd'g 

Ht. 

Tab.  I. 

Neversink 
Blue  Mt.. 
Neversink 

1030P.M. 

3  PM. 

6 

28.90 

27.47 
28.85 

60° 
60° 
64° 

28.87 

27.47 

1941 
3295 

60  +  62-100 
1000 


Diff.  =  (3295- 1941 ) 

--=1354x1.022 

—  1384   feet   above   Neversink   or 

2734  feet  above  the  sea. 
The  corrected  reading  would  be  28.875, 
if  the  second  reading  had  been  midway 
in  point  of  time  between  the  first  and 
last. 

This  mountain  is  in  Ulster  Co.,  N.  Y. 
Long.  74°  35  "W..  and  Lat.  41°  52  N. 


Neversink    and 
(Casella  Aneroid). 


Denman    Mountains 
September  11,  1880. 


Time. 

Bar. 
Rd'g 

T. 

Cor. 
Rd'g 

Ht. 
Tab.I. 

Neversink 
1).  Mt.... 
Neversink 

12.  30  A  M. 
4.30     " 
9 

28  86 
27.13 

28.82 

70 
63 
55 

28.84 
27.13 

1969 
3634 

74 


=  1665x1.026 

=1708   feet   above   Neversink  or 
3058  feet  above  the  sea. 

This  mountain  is  S.  S.  W.  of  Slide 
Mountain,  and  near  Claraville.  Long. 
74°  28';  Lat.  41°  53'  N. 


Fryeburg,  Me.,  and  Kiarsarge  Mount- 
ain, N.  H. — Fryeburg  base  434  feet 
above  the  sea,  July  9th,  1881. 

(Casella  Aneroid] 


Time. 

Bar. 

Readings 

rp        !       Jit. 

Tab.L 

Fryeburg.  .  . 
Kiarsarge.  . 

6  A.  M. 
....   IP.  M. 

29.63 
26.83 

66°     1233 
74°    3938 

(Note) — Barometer    at   Fryeburg    re- 
mained stationary. 


=2813  feet 

or  3247  feet  above  the  sea. 


75 


Fryeburg,    Me.,   and   Mt.    Kiarsarge, 
N.  H.  (second  survey)  August  17th,  1881. 
( Casella  A  nero id. ) 


Time. 

Bar.      |  T 
Readings 

Ht. 
Tab.  I. 

Fryeburg  

9  A.M, 

29.70      59° 

1169 

Mt.  Kiarsarge.  .  . 

3P.M. 

26.81       53° 

3958 

(Note) — Barometer  at   Fryeburg  sta- 
tionary till  4  P.  M. 

Diff.  =  2,789x1.012=2822  feet. 
Total  ht.= 3256  feet  above  the  sea. 
Height  of  this  summit  according  to  the 
Geological  Survey  is  3251  feet. 


Liberty  Hill,  N.  H.  (near  Laconia), 
and  Mt.  Belknap. — The  base  station  was 
at  Mr.  Howe's  1130  feet  above  the  sea, 
July  9th,  1878. 

(Casella  Barometer.} 


Bar. 
Readings. 

T. 

Ht. 
Tab.  I. 

Liberty  Hill.  .... 
lit.  Belknap  

28.75 
27.53 

82° 
78° 

2054 
3235 

76 

As  the  interval  between  the  observa- 
tions was  very  short,  and  the  general 
pressure  sensibly  stationary,  no  record 
was  made  of  the  time  nor  the  return 
reading. 

82  +  78-100 


Diff.  =  (3235  -2054)(l  +  * 


1000 
=  1252  feet 

or  2382  feet  above  the  sea. 
(Note) — An  average  of  three  measure- 
ments of  this  mountain  gave  2392  feet. 
The   other   observations   yielding    2369 
and  2425  ft.  respectively. 

The  height  given  in  the  Guide  Books 
quoted  from  the  Geological  Survey  is 
2394  feet. 


77 


CHAPTER  Y. 

SUGGESTIONS    IN   REGARD    TO    THE    SELECTION 
AND  SYSTEMATIC  USE  OF  AN  ANEROID. 

Dealers  in  good  aneroids  are  generally 
prepared  to  testify  in  regard  to  the  per- 
formance of  their  instruments  when 
tested  by  the  air  pump.  Comparison 
tables  frequently  accompany  first-class 
instruments  which  show  the  differences 
between  the  aneroid  referred  to  and  a 
standard  mercurial  barometer  submitted 
to  the  same  exhaustion. 

The  buyer  may  reasonably  ask,  there- 
fore, that  such  a  .test  may  be  made  if  it 
has  not  been  previously  done. 

The  best  English  aneroids  are  now 
marked  compensated,  and  are  presumably 
free  from  error  arising  from  changes  of 
temperature  in  the  instrument  itself. 
Whether  such  be  the  case  can  readily  be 
determined,  by  the  owner  of  the  instru- 
ment subjecting  it  to  the  action  of  a 


78 


freezing  mixture  and  then  of  a  drying 
oven,  while  the  normal  pressure  remains 
the  same.  A  thermometer  should  be 
placed  beside  the  aneroid  during  the 
trial.  A  range  of  temperature  from  15° 
F.  to  175°  F,  may  easily  be  produced, 
and  a  co- efficient  of  correction  if  the  in- 
strument is  not  compensated,  may  be 
determined. 

The  graduations  of  a  good  instrument 
are  neatly  engraved  on  the  dial. 

The  divisions  corresponding  to  the 
inches  and  fractions  of  a  mercurial  bar- 
ometer are  the  only  essential  ones.  The 
circle  of  feet,  whether  movable  or  fixed, 
is  a  convenience  of  secondary  import- 
ance; 

If  an  aneroid  bears  a  fixed  circle  of 
feet  with  the  zero  mark  corresponding  to 
the  30-inch  point  of  the  other  scale,  the 
probabilities  are  that  the  instrument  is 
not  from  one  of  the  best  makers. 

Excellent  aneroids  are  now  made  with 
dial  plates  only  2^-  inches  in  diameter. 
The  Casella  barometer  referred  to  in  the 
examples  has  a  diameter  of  only  1^ 


79 

inches.  Of  course  the  smaller  fractions 
of  an  inch  are  more  easily  read  on  dials 
of  4  inches  in  diameter ;  but  the  porta- 
bility of  the  smaller  instruments  recom- 
mends them  for  the  use  of  the  topogra- 
pher, and  the  medium  size,  which  is  from 
2J  to  2^-  inches,  is  now  most  in  demand 
for  surveyor's  work. 

The  aneroids  in  any  considerable 
collection  will  be  found  to  be  vari- 
ously graduated  ;  some  of  them  capable 
of  indicating  a  fall  of  pressure  to  20 
inches,  corresponding  to  a  height  of  over 
11,000  feet,  while  many  are  designed  for 
continual  use  below  3,000  feet  of  alti- 
tude. In  two  instruments  of  the  same 
diameter,  but  differing  as  above,  it  is 
clear  that  the  latter  will  have  the  larger 
scale  divisions,  and  will,  therefore,  be 
the  better  instrument  to  use  at  the 
lower  altitudes. 

It  should  be  carefully  remembered 
that  all  aneroids  vary  in  their  readings, 
with  the  position  in  which  they  are  held; 
reading  always  a  little  higher  with  the 
dial  horizontal  (face  uppermost),  than 


80 

when  it  is  vertical.  The  difference  is 
clearly  owing  to  the  direct  weight  of  the 
mechanism  exerted  on  the  vacuum  box. 
There  is  no  objection  to  allowing  this 
weight  to  be  always  added,  but  the  prac- 
tice of  the  observer  should  be  uniform, 
and  to  read  from  the  horizontal  dial  is 
probably  the  most  convenient  practice. 

A  tap  with  the  finger  just  before  tak- 
ing the  reading  is  required  to  bring  the 
springs  to  their  proper  bearing.  Also, 
in  case  of  rapid  ascents,  as  some  aneroids 
will  not,  at  the  moment  of  attaining  an 
altitude,  indicate  the  entire  fall  of  press- 
ure, a  few  minutes'  delay  is  necessary. 

The  pointer  should  be  fine  and  very 
close  to  the  graduated  scale,  and  the 
reading  should  be  taken  by  looking  along 
the  direction  of  the  pointer. 

For  ordinary  work  it  should  not  be 
considered  important  to  adjust  the 
aneroid  to  an  absolute  agreement  with 
the  mercurial  barometer.  The  difference 
between  the  readings  may  be  noted,  but 
to  force  the  aneroid  to  an  agreement  by 


81 

aid  of  the  adjusting  screw  is  a  question- 
able practice. 

Whenever  comparison  with  the  mer- 
cury column  is  made,  the  reduction  for 
the  latter  by  Table  4  should  be  carefully 
observed. 

In  the  use  of  either  form  of  Aneroid, 
whether  it  has  been  furnished  with  a 
correction  table  or  not,  the  observer 
should  take  early  means  to  become  ac- 
quainted with  its  limits  of  error  under 
various  conditions  of  temperature  or 
pressure.  Repeated  measurements  of  a 
known  altitude  afford  good  data  for  such 
information,  but  direct  comparisons,  for 
a  long  time,  with  a  standard  cistern 
barometer  will  yield,  with  a  minimum  of 
labor,  the  greatest  number  of  compari- 
sons. 

For  the  method  of  dealing  with  such 
data  to  determine  correction  coefficients, 
the  reader  is  referred  to  the  larger  treati- 
ses, the  most  exhaustive  of  which,  prob- 
bly,  is  "  Die  Aneroide,"  by  Josef  Holt 
schl  (Alfred  Holder,  Vienna,  1872). 

For  ordinary  use   of  a    single  instru- 


82 

ment,  however,  the  corrections,  if  any 
are  necessary,  are  determined  with  suffi- 
cient accuracy  by  the  exercise  of  ordi- 
nary skill  and  patience ;  skill  here  imply- 
ing, also,  systematic  trial. 

Some  of  the  sources  of  error  in  meas- 
uring altitudes,  which  are  not  to  be  elimi- 
nated by  any  adjustment  or  correction  of 
instruments,  are  clearly  stated  by  Prof. 
Elias  Loomis,  in  a  paper  read  before  the 
National  Academy  of  Sciences,  April  19, 
1881. 

"The  Laplace  formula  assumes*  that 
the  atmosphere  has  attained  a  condition 
of  equilibrium,  and  in  such  a  case  it  gives 
the  reduction  to  sea  level  with  tolerable 
accuracy.  The  average  of  a  long  series 
of  observations  represents  approximate- 
ly such  a  condition  of  equilibrium ;  but 
in  the  daily  observations  this  equilibrium 
is  very  much  disturbed.  The  mean  be- 
tween the  temperatures  at  the  upper 
and  lower  stations  does  not  represent  the 
average  temperature  of  the  intermediate 
column  of  air ;  and  when  the  atmos- 
phere is  in  rapid  motion  the  downward 


83 

pressure  is  modified  by  the  earth's  rota- 
tion, in  a  manner  not  represented  by  the 
Laplace  formula.  There  is  no  doubt 
that  the  formulae  of  reduction  now  em- 
ployed may  be  considerably  improved ; 
but  it  does  not  seem  possible  that  any 
single  formula,  with  constant  coefficients, 
,  should  provide  for  the  immense  variety 
of  conditions  which  prevail  in  the  neigh- 
borhood of  mountain  stations ;  and  we 
may  be  compelled  for  each  mountain  re- 
gion to  adopt  tables  founded  upon  a  di- 
rect comparison  of  observations  made  at 
stations  of  different  elevations  and  not 
very  remote  from  each  other." 

The  following  remarks  bearing  upon 
the  same  subject  are  from  an  article  by 
J.  Allan  Brown,  F.  K.  S.,  on  "  Periodic 
Oscillations  of  Barometric  Pressure,*' 
published  in  Nature  in  April,  1881 : 

Sedgwick  has  said :  ["  To  explain  dif- 
ficulties in  these  questions  "  (relating  to 
pressure  and  temperature)  "the  atmos- 
pheric strata  have  been  shuffled  in  accord- 
ance with  laboratory  experience."] 

"  If  we  suppose  that  the  attraction  of 


gravity  is  not  the  only  attraction  which 
affects  the  pressure  of  the  atmosphere, 
but  that  this  pressure  varies  through 
some  other  attracting  force — such  as  an 
electric  attraction  of  the  sun  depending 
upon  the  varying  humidity  of  the  air,  and 
this  again  depending  on  its  tempera- 
ture, we  should  find  another  method  of 
relating  the  two  variations  which  does 
not  exist  if  gravitation  alone  is  employed. 
It  is  quite  certain  that  many  physicists 
will  not  admit  the  idea  of  an  electric  at- 
traction on  our  atmosphere  in  the  present 
state  of  our  knowledge,  hence  the  efforts 
to  make  expansion,  and  a  shuffling  of  the 
atmospheric  strata  suffice.  We  must 
not,  however,  in  our  ignorance,  attempt 
to  force  conclusions  in  opposition  to 
facts,  and  if  these  can  be  satisfied  more 
easily  and  with  greater  probabilities  in 
its  favor  by  the  aid  of  the  hypothesis  of 
an  electric  attraction  of  the  sun,  that 
hypothesis  will  have  a  better  claim  to 
acceptance  than  the  other.  I  shall  here 
note  a  few  facts  which  cannot  be  explain- 
ed by  thermic  actions. 


85 

"  1.  I  have  shown  that,  on  the  average  of 
many  years'  observation  in  our  latitudes, 
the  mean  pressure  diminishes  at  the  rate 
of  0".038  of  mercury  for  every  one  hun- 
dred miles  we  proceed  toward  the  north. 
This  has  been  called  a  gradient  from  the 
the  similar  term  used  in  railway  slopes: 
but  it  is  no  slope,  it  is  a  level  of  a  sur- 
face of  equilibrium  like  that  of  the  sea. 
It  is  the  mean  heights  of  the  barometer 
at  the  sea  level  which  indicate  the  form, 
if  we  may  so  say,  of  the  equilibrating  at- 
mosphere. 

"  2.  In  India  we  have  seen  that  the  at- 
mospheric pressure  oscillates  at  each 
station  even  when  these  are  quite  near  to 
each  other,  independently  of  the  known 
laws  of  equilibrium  of  gases.  When  we 
"turn  to  the  semi-diurnal  oscillation  of 
the  barometer  we  are  only  amused  at  the 
attempts  made  to  explain  it  by  shuffling 
the  atmospheric  strata.  Nothing  can  be 
more  certain  than  that  the  theories  of 
expansion,  or  resistance  to  expansion  and 
overflow,  are  the  vain  efforts  to  make  the 
laws  of  nature  agree  with  a  theory.  Over 


86 


the  great  ocean  within  the  tropics,  where 
the  diurnal  variations  of  temperature  are 
small  and  the  air.  is  absolutely  without 
perceptible  currents  for  days  together, 
the  barometer  rises  and  falls  a  tenth  of 
an  inch  twice  in  twenty -four  hours  with 
the  regularity  of  the  solar  clock.  The 
action  of  the  sun  on  the  whole  atmos- 
phere which  produces  this  movement 
varies  chiefly  during  the  day  hours  at  in- 
land stations  with  the  temperature  oscil- 
lation, so  that,  as  in  the  case  of  the 
annual  variation,  the  fall  of  the  barometer 
at  4  P.  M.  is  greater  in  the  same  latitude 
as  the  temperature  is  higher.  This 
variation  occurs  during  the  most  com- 
plete calms;  the  smoke  rises  vertically 
from  the  plain  of  Tinnevelly ;  no  current 
is  visible  in  the  motion  of  the  clouds;  yet 
the  barometer  falls  at  four  in  the  morn- 
ing as  it  did  at  four  in  the  afternoon, 
only  it  falls  less." 

It  seems  probable  that  the  use  of  the 
Aneroid  will  soon  become  more  widely 
extended,  and  that  engineers,  when  made 
familiar  with  the  qualities  of  well-made 


87 


instruments,  will  welcome  so  valuable  an 
aid  in  preliminary  surveys.  The  condi- 
tions of  satisfactory  work  with  baro- 
meters are  certainly  peculiar,  and  to  field 
workers  familiar  only  with  the  level  and 
transit,  may  seem  unique.  But  when 
the  conditions  are  fully  understood,  the 
engineer  may  easily  take  precautions 
which  will  avoid  too  large  errors,  and 
conduct  surveys  in  hilly  regions  with 
acelerity  not  heretofore  attained. 


88 


TABLE  I. 

FOR   ESTIMATING    HEIGHTS    BY   THE   ANEROID. 

Take  readings  of  the  barometer  and  thermom- 
eter at  both  stations  ;  find  in  the  table  the 
heights  corresponding  to  the  barometric 
readings,  and  subtract  them.  Multiply  the 

T  and  t  being 


- 
remainder  by  1+  —  J 


the  temperatures,  the  product  will  be  the 
difference  in  altitude. 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches 

Feet. 

Inches. 

Feet. 

31.00 

00 

30.81 

168 

30.99 

9 

30.80 

177 

80.98 

18 

30.79 

186 

80.97 

27 

30.78 

195 

30.96 

85 

30.77 

203 

80.95 

44 

30.76 

212 

30.94 

53 

30.75 

221 

30.93 

62 

30.74 

230 

30.92 

71 

30.73 

239 

30.91 

80 

30.72 

247 

30.90 

88 

30.71 

256 

30.89 

97 

30.70 

265 

30.88 

106 

30.69 

274 

30.87 

115 

30.68 

283 

30.86 

124 

30.67 

292 

30.85 

133 

30.66 

301 

30.84 

142 

30.65 

310 

30.83 

151 

30.64 

318 

30.82 

160 

30.63 

827 

89 


Barometer    TT  .   ,  , 
Readings.     He'SQts- 

Barometer    TT  •  K+ 
Readings.  i  He'Shts- 

Inches.          Feet. 

Inches.          Feet. 

80.62 

336 

30.30 

622 

30.61 

345 

30.29 

631 

30.60 

354 

30.28 

640 

30.59 

363 

30.27 

649 

30.58 

372 

30.26 

658 

30.57 

381 

30.25 

667 

30.56 

390 

30.24 

676 

30.55 

399 

30.23 

685 

30.54 

407 

30.22 

694 

30.53 

416 

30.21 

703 

80.52 

425 

30.20 

712 

30.51 

434 

30.19 

721 

30.50 

443               30.18 

730 

30.49 

452               30.17 

740 

30.48 

461               30.16 

749 

30.47 

470 

30.15 

758 

30.46 

479 

30.14 

767 

30.45 

488 

30.13 

776 

30.44 

497 

30.12 

785 

30.43 

506 

30.11 

794 

30.42 

515 

30.10 

803 

30.41 

524 

30.09 

812 

30.40 

533 

30.08 

821 

30.39 

542 

30.07 

830 

30.38 

551 

30.06 

839 

30.37 

559 

80  05 

849 

30.38 

569 

30.04 

857 

30  35 

578 

30.03 

866 

30.34 

587 

30.02 

875 

30.33 

596 

30.01               884 

30.32 

605 

30.00               893 

30.31 

613 

29.99               903 

90 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet. 

Inches. 

Feet. 

29.98 

911 

29.66 

1205 

29.97 

920               29.65 

1214 

29.96 

929               29.64 

1224 

29.95               938               29.63 

1233 

29.94 

947 

29.62             1242 

29  93 

956 

29.61             1251 

29.92 

965 

29.60          .    1260 

29.91 

97(5 

29.59             1269 

29.90 

985 

29.58 

1278 

2).  89 

994 

29.57             1287 

29.88 

1002 

29.56 

1296 

29.87 

1012 

29.55             1305 

29.86 

1021 

29.54             1314 

29.85 

1030 

29.53 

1824 

29.84 

1039 

25.52             1333 

29.83 

1049 

29.51             1342 

29.82 

1058 

29.50             1352 

29.81 

1067 

29.49             1361 

29.80 

1076 

29.48             1370 

29.79 

1085 

29.47             1379 

29.78 

1094 

29.46 

1389 

29.77 

1103 

29.45             1398 

29.76 

1113 

29.44             1408 

29  75 

1122 

29.43             1417 

29.74 

1132 

29  42             1426 

29.73 

1141 

29.41 

1435 

29.72 

1150 

29.40 

1445 

29.71 

1159 

29.39             1454 

29.70 

1169 

29.38             1464 

29  69 

1177 

29.37             1473 

29.68 

1186 

29.36             1482 

29.67 

1195 

29.35             1491 

91 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches 

Feet. 

Inohes. 

Feet. 

29.34 

1500 

29.02 

1799 

29.33 

1509 

29.01 

1809 

29.32 

1519 

29.00 

1818 

29.31 

1528 

28.99 

1827 

29.30 

1537 

28.98 

1837 

29  29 

1546 

28.97 

1846 

29.28 

1556* 

28.96 

1856 

29.27 

1565 

28.95 

1865 

29.26 

1574 

28.94 

1875 

29.25 

1583 

28.93 

1884 

29.24 

1593 

28.92 

1894 

29.23 

1603 

28.91 

1903 

29.22 

1612 

28.90 

1913 

29.21 

1621 

28.89 

,  1922 

29.20 

1630 

28.88 

*  1931 

29.19 

1639 

28.87 

1941 

29.18 

1649 

28.86 

1950 

29  17 

1658 

28.85 

1960 

29.16 

1668 

28.84 

1969 

29.15 

1677 

28.83 

1979 

29.14 

1687 

28.82 

1988 

29.13 

1696 

28.81 

1998 

29.12 

1706 

28.80 

2007 

29.11 

1715 

28.79 

2016 

29.10 

1725 

28.78 

2026 

29.09 

1734 

28.77 

2035 

29.08 

1743 

28.76 

2044 

29.07 

1752 

28.75 

2054 

29.06 

1762 

28.74 

2063 

29.05 

1771 

28.73 

2073 

29.04 

1781 

28.72 

2082 

29.03 

1790 

28  71 

2091 

92 


Heights. 

Barometer 
Readings. 

Heights. 

Inches.          Feet. 

Inches. 

Feet. 

28.70            2101 

28.38 

2407 

28.69            2111 

28.37 

2416 

28.68            2120 

28.36 

2426 

28.67 

2129 

28.35 

2435 

28.66 

2139 

28.34 

2445 

28  65 

2148 

28  33 

2455 

28.64 

2158 

28.32 

2464 

28.63 

2168 

28  31 

2474 

28.62 

2177 

28.30 

2483 

28.61 

2186 

28.29 

2493 

28.60 

2196 

28.28 

2503 

28.59 

2205 

28.27 

2512 

28.58 

2215 

28.26 

2522 

28.57 

.  2224 

28.25 

.     2531 

28.56 

2234 

28.24 

2541 

28.55 

2243 

28.23 

2551 

28.54 

2253 

28.22 

2561 

28.53 

2263 

28.21 

2570 

28.52 

2272 

28.20 

2580 

28.  ni 

2282 

28.19 

2590 

28.50 

2291 

28.18 

2600 

28.49 

2301 

28.17 

2609 

28.48 

2310 

28  16 

2619 

28.47 

2320 

28.15 

2628 

28.46 

2329 

28.14 

2638 

28.45 

2339 

28.13 

2648 

28.44 

2349 

28.12 

2658 

28.43 

2358 

28.11 

2667 

28.42 

2368 

28.10 

2677 

28.41 

2378 

28.09 

2687 

28.40 

2387 

28.08 

•    2696 

28.39 

2397 

28.07 

2706 

i 

93 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet, 

Inches.    \      Feet. 

28.06 

2715 

27.74            3029 

28.05 

2726 

27.73            3039 

28.04 

2735 

27.72 

3048 

28.03 

2745 

27.71 

3058 

28.02 

2755 

27.70 

3068 

28  01 

2765 

27.69 

3078 

28.00 

2774 

27.68 

3087 

27.99 

2784 

27.67 

3097 

27.98 

2794 

27.66 

3107 

27.97 

2804 

27.65 

3117 

27.96 

2813 

27.64 

3126 

27.95 

2823 

27.63 

3136 

27.94 

2833 

27.62 

3146 

27.93 

2843 

27.61 

3156 

27.92 

2853 

27.60 

3166 

27  91 

2863 

27.59 

3176 

27  90 

2873 

27.58 

3186 

27.89 

2882 

27.57 

3196 

27.88 

2892 

27.56 

3206 

27.87 

2901 

27  55 

3216 

27.86 

2911 

27.54 

3225 

27.85 

2921 

27.53 

3235 

27.84 

2930 

•      27.52 

3245 

27.83 

2940 

27.51 

3255 

27.82 

2950 

27.50 

3265 

27.81 

2960 

27.49 

3275 

27.80 

2969 

27.48 

3285 

27.79 

2979 

27.47 

3295 

27.78 

2989 

27.46 

3305 

27.77 

2999 

27.45 

3315 

27.76 

3009 

27.44 

3325 

27.75 

3019                27.43 

3335 

94 


"Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet. 

Inches. 

Feet, 

27.42 

3345 

27.10 

3665 

27.41 

3355 

27.09 

3675 

27.40 

3365 

27.08 

3685 

•27.39 

3375 

27.07 

3695 

27.38 

3384 

27.06 

3705 

27.37 

3394 

27.05 

3715 

27.36 

3404 

27.04 

3725 

27.35 

3414 

27.03 

3785 

27.34 

3424 

27.02 

3745 

27.33 

3434 

27.01 

3755 

27.32 

3444 

27.00 

3765 

27.31 

3454 

26.99 

3775 

27.30            3464 

26.98 

3785 

27.29 

3474 

26.97 

3795 

27.28 

3484 

26.96 

3806 

27.27            3494 

26.95 

"  3816 

27.26 

3504 

26.94 

3826 

27.25 

3514 

26.93 

3836 

27.24 

3524 

26.92 

3846 

27.23 

3534 

26.91 

3856 

27.22 

3544 

26.90 

3866 

27.21 

3554 

26.89 

3876 

27.20 

3564 

26  88 

3886 

27.19 

3574 

26.87 

3897 

27.18 

3584 

26.86 

3907 

27  17 

3594 

26.85 

3917 

27.16 

3604 

26.84 

3927 

27.15 

3614 

26.83 

3038 

27.14 

3624 

26.82 

3948 

27.13 

3634 

26.81 

3958 

27  12 

3644 

26.80 

,  .  3068 

27.11 

3654 

26.79 

3978 

,   95 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet, 

Inches. 

Feet. 

26.78 

3988 

26.46 

4315 

26.77 

3999 

26,45 

4326 

25.76 

4009 

26.44 

4336 

26  75 

4019 

26.43 

4347 

26.74 

4030 

26.42 

4357 

26.73 

4040 

26.41 

431J8 

26.72 

4050 

26.40 

4378 

26.  7L 

4060 

26.39 

4388 

26.70 

4070 

26.38 

.4399 

26.69 

4081 

26.37 

4409 

26.68 

4091 

26.36 

4419 

,  26.<)7 

4101 

26.35 

4430 

26.66 

4111 

26.34 

4440 

26.65 

4122 

26.33 

4450 

26.64 

4132 

26.32 

4461 

26.63 

4142 

26.31 

4472 

26.62 

4152 

26.30 

4482 

26.61 

4163 

26.29  ' 

4492 

26  .  (50 

4173 

26.28 

4502 

26.59 

4183. 

26.27 

4513 

26.58 

4193 

26.26 

4523 

26.57 

4203 

26.25 

4533 

26.56 

4213 

26.24 

4544 

26.55 

4223 

26.23 

4554 

26.54 

4233 

26.22 

4565 

26.53 

4244 

26.21 

4575 

26.52 

4254 

26.20 

4585 

26.51 

4264 

26.19 

4596 

26.50 

4274 

26.18 

4606 

26.49 

4284 

26.17 

4617 

36  .  48 

4294 

26.16 

4627 

26.47 

4304              26.15 

4638 

96 


Barometer    H  .  , 
Readings.      Iei£hts- 

Barometer 
Readings. 

Heights. 

Inches.          Feet. 

Inches. 

Feet, 

26.14            4648 

25.82 

4983 

26.13            4658 

25.81 

4994 

26.12            4669 

25.80 

5004 

26.11            4679 

25.79 

5014 

26.10            4690 

25.78            5025 

26.09            4700 

25.77            5036 

26.08            4711 

25.76 

5046 

26.07 

4721 

25.75            5057 

26.06 

4731 

25.74 

5067 

26.05 

4742 

25.73 

5078 

26.04 

4752 

25.72            5088 

23.03 

4763 

25.71            5099 

28.02 

4773 

25.70            5110 

26.01 

4784 

25.69            5121 

26.00 

4794 

25.68            5132 

25.99 

4805 

25.67            5142 

25.98 

4815 

25.66            5153 

25.97 

4826 

25.65            5164 

25.96 

4836 

25.64 

5174 

25.95 

4847 

25.63 

5185 

25.94 

4857 

25.62            5195 

25.93 

4868 

25.61            5206 

25.92 

4878 

25.60            5216 

25,91 

4889 

25.59            5227 

25.90 

4899 

25.58            5237 

25.89 

4910 

25.57            5248 

25.88 

4920 

25.56            5259 

25.87 

4931 

25.55            5270 

25.86 

4941 

25.54            5281 

25.85 

4952 

25.53            5291 

25.84 

4962 

25.52            5302 

25.83 

4973 

25.51 

5312 

97 


Barometer 
Readings. 

TT  .   -.  .       i    Barometer 
Hei-rhts'        Readings. 

Heights. 

Inches          Feet.              Inches.          Feet. 

25.50            5323 

25.18            5668 

25.49            5333                25.17            5679 

25.48            5344               25  16            5689 

25.47            5355 

25.15            5700 

25.46            5365 

25.14            5711 

25.45 

5376 

25.13 

5722 

25.44 

5387 

25.12 

5733 

25.43 

5397 

25.11 

5744 

25.42 

5408 

25.10 

5754 

25.41 

5419 

25.09 

5765 

25.40 

5429 

25.08 

5776 

25  39 

5440 

25.07 

5787 

25.38 

5451 

25.06 

5798 

25.37 

5462 

25.05 

5809 

25.36 

5473 

25.04 

5820 

25.35 

5483 

25.03 

5831 

25.34 

5494 

25.02 

5842 

25.33 

5505 

25.01 

5853 

25.32 

5516 

25.00 

5863 

25.31 

5527- 

24.99 

5874 

25.30 

5537 

24.98 

5885 

25  29 

5548 

24.97 

5896 

25.28 

5559 

24.96 

5907 

25.27 

5570 

24.95 

5918 

25.26 

5581 

24.94 

5929 

25.25 

5592 

24.93 

5940 

25.24 

5602 

24.92 

5950 

25.23 

5613 

24.91 

5962 

25.22 

5624 

24.90 

5972 

25.21 

5635 

24.89 

5983 

25.20 

5646 

24.88 

5994 

25.19 

5657 

24.87 

6005 

98 


I 

Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet. 

Inches. 

Feet. 

24.86 

6016 

24.54 

6368 

24.85 

6027 

24.53 

6379 

24.84 

6038 

24.52 

6390 

24.83 

6049 

24.51 

6401 

24.82 

6060 

24.50 

6412 

24.81 

6071 

24.49 

6424 

24.80 

6082 

24.48 

6435 

24.79 

6093 

24/47 

6446 

24.78 

6104 

24.46 

6458 

24.77 

6115 

'     24.45 

6469 

24.76 

6126 

24.44 

6480 

24.75 

6137 

24.43 

6491 

24.74 

6148 

24.42 

6503 

24,73 

6159 

24.41 

6514 

24.72 

6170 

24.40 

6525 

24.71 

6181 

24.39 

6536 

24.70 

6192 

24.38 

6547 

24.69 

6203 

24.37 

6559 

24.68 

6214 

24.36 

6570 

24.67 

6225 

24.35 

6581 

24.66 

6236 

24.34 

6592 

24.65 

6247 

24.33 

6603 

24.64 

6258 

24.32 

6615 

24.63 

6269 

24.31 

6626 

24.62 

6280 

24.30 

6637 

24.61 

6291 

24.29 

6648 

24.60 

6302 

24.28 

6659 

24.59 

6313 

24.27 

6671 

24.58 

6324 

24.26 

6682 

24.57 

6335 

24.25 

6693 

24.56 

6346 

24.24 

6705 

24.55 

6357 

24.23 

6716 

99 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet. 

Inches. 

Feet. 

24.  22 

6727 

23.90 

7090 

24.21 

6738 

23.89 

7101 

24.20 

6750 

23.88 

7113 

24.19 

6761 

23.87 

7124 

24.18 

6772 

23.86 

7135 

24.17 

6783 

23.85 

7146 

24.16 

6795 

23.84 

7157 

24.15 

6806 

23.83 

7168 

24.14 

6817 

23.82 

7180 

24.13 

6828 

23.81 

7191 

24.12 

6840 

23.80 

7203 

24.11 

6851 

23.79 

7214 

24.10 

6862 

23.78 

7226 

24.09 

6873 

23.77 

7237 

24.08 

6885 

23.76 

7249 

24.07 

6896 

23.75 

7261 

24.06 

6907 

23.74 

7272 

24.05 

6919 

23.73 

7283 

24.04 

6930 

23.72 

7294 

24.03 

6941  . 

23.71 

7305 

24.02 

6953 

23.70 

7316 

24.01 

6964 

23.69 

7327 

24.00 

6976 

23.68 

7339 

23.99 

6987 

23.67 

7350 

23.98 

6999 

23.66 

7362 

23.97 

7010 

23.65 

7374 

23.96 

7022 

23.64 

7386 

23.95 

7033 

23.63 

7398 

23.94 

7045 

23.62 

7409 

23.93 

7056 

23.61 

7421 

23.92 

7068 

23.60 

7433 

23.91 

7079 

23.59 

7445 

[ 

100 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet. 

Inches. 

Feet. 

23.58 

7456 

23.26 

7829 

23.57 

7468 

23.25 

7841 

23.56 

7480 

23.24 

7853 

23.55 

7492 

23.23 

7865 

23.54 

7503 

28.22 

7876 

23.53 

7515 

23.21 

7888 

23.52 

7527 

23.20 

7900 

23.51 

7539 

23.19 

7912 

23.50 

7550 

23.18 

7923 

23.49 

7562 

23.17 

7935 

23.48 

7574 

23.16 

7946 

23.47 

7585 

23.15 

7958 

23.46 

7597 

23.14 

7969 

23.45 

7609 

23.13 

7981 

23  44 

7621 

23.12 

7092 

23.43 

7633 

23.11 

8004 

23.42 

7644 

23.10 

8015 

23.41 

7656 

23.09 

8027 

23.40 

7667 

23.08 

8039 

23.39 

7679 

23.07 

8051 

23.38 

7690 

23.06 

8063 

23.37 

7702 

23.05 

8075 

23.36 

7713 

23.04 

8086 

23.35 

7725 

23.03 

8098 

23.34 

7736 

23.02 

8110 

23.33 

7748 

23.01 

8122 

23.32 

7759 

23.00 

8134 

23.31 

7771 

22.99 

8146 

23.30 

7782 

22.98 

8158 

23.29 

7793 

22.97 

8170 

23.28 

7805 

22.96 

8182 

23.27 

7817 

i 

22.95 

8194 

101 


Barometer 
Reading?. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet. 

Inches. 

Feet. 

22.94 

8206 

22.62 

8591 

22.93 

8218 

22.61 

8603 

22.92 

8-^30 

22.60 

8615 

22.91 

8242 

22.59 

8627 

22.90 

8254 

23.58 

8638 

22.89 

8266 

22.57 

8650 

22.88 

8278 

22.56 

8661 

22.87 

8290 

22.55 

8673 

22.86 

8302 

22.54 

8685 

22.85 

8314 

22.53 

8697 

22.84 

8326 

22.52 

8709 

22.83 

8338 

22.51 

8721 

22.82 

8350 

22.50 

8733 

22.81 

8362 

22.49 

8745 

22.80 

8374 

22.48 

8757 

22.79 

8386 

22.47 

8769 

22.78 

8398 

22.46 

8781 

22.77 

8410 

22.45 

8793 

22.76 

8422 

22.44 

8806 

22.75 

8434 

22.43 

8818 

22.74 

8446 

22.42 

8830 

22.73 

8458 

22.41 

8842 

22.72 

8470 

22.40 

8855 

22.71 

8482 

22.39 

8867 

22.70 

8495 

22.38 

8879 

22.69 

8507 

22.37 

8891 

22.68 

8519 

22.36 

8904 

22.67 

8531 

22.35 

8916 

22.66 

8543 

22.34 

8928 

22.65 

8555 

22.33 

8941 

22.64 

8567 

22.32 

8953 

22.63 

8579 

22.31 

8965 

102 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet. 

Inches. 

Feet. 

22.30 

8977 

21.98 

9372 

22.29 

8090 

21.97 

9384 

22.28 

9002 

21.96 

9397 

22.27 

9014 

21.95 

9410 

22.26 

9026 

21.94 

9422 

22.25 

9039 

21.93 

9435 

22.24 

9051 

21.92 

9447 

22.23 

9063 

21.91 

9460 

22.22 

9075 

21.90 

9472 

22.21 

9088 

21.89 

9485 

22.20 

9100 

21.88 

9497 

22.19 

9113 

21.87 

9510 

22.18 

9125 

21.86 

9522 

22.17 

9138 

21.85 

9535 

22.16 

9150 

21.84 

9547 

22.15 

9162 

21.83 

9560 

22.14            9174 

21.82 

9572 

22.13 

9187 

21.81 

9585 

22.12 

9199 

21.80 

9597 

22.11 

9212 

21.79 

9610 

22.10 

9224 

21.78 

9622 

22.09 

9236 

21.77 

9635 

22.08 

9249 

21.76 

9647 

22.07 

9262 

21.75 

9660 

23.06 

9274 

21.74 

9672 

22.05 

9286 

21.73 

9685 

22.04 

9298 

21.72 

9697 

22.03 

9311 

21.71 

9710 

22.02 

9323 

21.70 

9722 

22.01 

9336 

21.69 

9735 

22.00 

9348 

21.68 

9747 

21.99 

9360 

21.67 

9760 

103 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet. 

Inches. 

Feet. 

21.66 

9772 

21.34 

10176 

21.65 

9785 

21.33 

10189 

21.64 

9797 

21.32 

10202 

21.63 

9810 

21.31 

10214 

21.62 

9822 

21.30 

10228 

21.61 

9835 

21.29 

10241 

21.60 

9848 

21.28 

10253 

21.59 

9861 

21.27 

10266 

21.58 

9873 

21.26 

10278 

21.57 

9886 

21.25 

10291 

21.56 

9898 

21.24 

10304 

21.55 

9911 

21.23 

10317 

21.54 

9923 

21.22 

10330 

21.53 

9936 

21.21 

10343 

21.52 

9949 

21.20 

10355 

21.51 

9962 

21.19 

10368 

21.50 

9974 

21.18     . 

10381 

21.49             9987 

21.17 

10394 

21.48             9999 

21.16 

10407 

21.47           10012 

21.15 

10420 

21.46           10025 

21.14 

10432 

21.45           10088 

21.13 

10445 

21.44 

10050 

21.12 

10458 

21.43 

10063 

21.11 

10471 

21.42 

10075 

21.10 

10484 

21.41 

10088 

21.09           10497 

21.40 

10101 

21.08 

10509 

21.39 

10114 

21.07 

10522 

21.38           10126 

21.06 

10535 

21.37           10139 

21.05 

10548 

21.36 

10151 

21.04 

10561 

21.35 

10164 

21.03 

10574 

104 


Barometer    TT  •  ^f 
Readings.    HelSbts- 


Inches. 
21.02 
21.01 
21.00 
20.99 
20.98 
20.97 
20.96 
20.95 
20.94 
20.93 
20.92 
20.91 
20.90 
20.89 
20.88 
20.87 
20.86 
20.85 
20.84 
20.83 
20.82 
20.81 
20.80 
20.79 
20.78 
20.77 
20.76 
20.75 
20.74 
20.73 
20.72 
20.71 


Feet. 
10587 
10600 
10613 
10627 
10640 
10654 
10667 
10681 
10694 
10707 
10720 
10733 
10746 
10759 
10772 
10785 
10798 
10811 
10824 
10837 
10850 
10863 
10876 
10889 
10902 
10915 
10928 
10941 
10954 
10967 
10980 
10993 


Barometer 
"Readings 

Heights. 

Inches. 

Feet. 

20.70 

11006 

20.69 

11019 

20.68 

11032 

20.67 

11045 

20.66 

11058 

20  65 

11071 

20.64 

11084 

20.63 

11097 

20.63 

11110 

20.61 

11123 

20.60 

11136 

20.59 

11149 

20.58 

11163 

20.57 

11176 

20.56 

11190 

20.55 

11204 

20.54 

11217 

20.53 

11230 

20.52 

11243 

20.51 

11257 

20.50 

11270 

20.49 

11284 

20.48 

11297 

20.47 

11311 

20  46 

11324 

20.45 

11338 

20.44 

11351 

20.43 

11364 

20.42 

11377 

20.41 

11391 

20.40 

11404 

20.39 

11418 

105 


Barometer 
Readings. 

Heights. 

Barometer 
Readings. 

Heights. 

Inches. 

Feet. 

Inches. 

Feet. 

20.38 

11431 

20.18 

11700 

20.37 

11444 

20.17           11714 

20.36 

11457 

20.16           11727 

20.35 

11470 

20.15           11741 

20.34 

11483 

20.14 

11754 

20.33 

11496 

20.13 

11768 

20.32 

11509 

20.12 

11781 

20.31 

11523 

20.11 

11795 

20.30 

11536 

20.10 

11808— 

20.29 

11550 

20.09 

11821 

20.28 

11563 

20.08 

11835 

20.2? 

11577 

20.07 

11859 

20.26 

11591 

20.06 

11863 

20.25 

11605 

20.05 

11877 

20.24      !      11618 

20.04 

11891 

20.23 

11632 

20.03 

11905 

20.22 

11645 

20.02 

11918 

20.21 

11659 

20.01 

11932 

20.20 

11673 

20.00 

1'1945 

20.19 

11687 

1  -  ..."  -  fa  3 

'  Z  i 

106 


The  following  table  is  to  be  used 
when  applying  the  modified  formula 
of  chapter  II: 

D=60000(log.B-log.£)(l+ 

RULE. — Find  in  the  table  the  loga- 
rithms of  the  barometer  readings  to 
hundredths  of  an  inch.  Subtract  these 
logarithms  and  multiply  the  remainder 
by  60000.  The  product  is  the  approx- 
imate difference  in  altitude  between  the 
two  stations.  To  apply  the  corrections 
for  temperature,  add  the  temperatures 
of  the  two  stations  and  subtract  60°. 
Increase  the  above  approximate  value  by 
-g^  of  itself  for  each  degree  of  excess 
above  60°.  If  the  sum  of  the  tempera- 
ture is  less  than  60°  diminish  the  value 
by  a  like  amount. 


107 
TABLE  II. 


Bar. 
Height. 

Log. 

Bar. 
Height. 

Log. 

2200 

3.34242 

2231 

3.34850 

01 

.34262 

32     .34869 

02 

.34282 

33     .34889 

03 

.34301 

34     .34908 

04 

.34321 

35 

.34928 

05 

.34341 

36 

.34947 

06 

.34361 

37     .34967 

07 

.34380 

38 

.34986 

08 

.34400 

39 

.35005 

09 

.34420 

40 

.35025 

10 

.84439 

41 

.35044 

11 

.34459 

42 

.35064 

12 

.34479 

43 

.35083 

13 

.34498 

44 

.35102 

14 

.34518 

45 

.35122 

15 

.34537 

46 

.35141' 

16 

.34557 

47 

.35160 

17 

.34577 

48 

.35180 

18 

.34596. 

49 

.35199 

19 

.34616 

50 

.35218 

20 

.34635 

51 

.35238 

21 

.34655 

52 

.35257 

22 

.34674 

53 

.35276 

23 

.  34694 

54 

.35295 

24 

.34713 

55 

.35315 

25 

.34733 

56 

.35334 

26 

.34753 

57 

.35353 

27 

.  34772 

58 

.35372 

28 

.34792 

59 

.35392 

29 

.34811 

60 

.35411 

30 

.34830 

61 

.35430 

108 


Bar. 
Height. 

Log. 

Bar. 
Height. 

Log. 

2262 

3.35449 

2295 

3.36078 

63 

.35468 

96  i   .36097 

64 

.35488 

97 

.36116 

65 

.35507 

98 

.36135 

66 

.35526 

99 

.36154 

67 

.35545 

2300 

.36173 

68 

.35564 

01 

.36192 

69 

.35583 

02 

.36211 

70 

.35603 

03 

.36229 

71 

.35622 

04 

.36248 

72  ' 

.35641 

05 

.36267 

73 

.35660 

06 

.36286 

74 

.35679 

07 

.36305 

75 

.35698 

08 

.36324 

76 

.35717 

09 

.36342 

77 

.35736 

10 

36361 

78 

.35755 

11 

.36380 

79 

.35774 

12 

.36399 

80 

.35793 

13 

.36418 

81 

.35813 

14 

.36436 

82 

.35832 

15 

.36455 

83 

.35851 

16 

.36474 

84 

.35870 

17 

.36493 

85 

.35889 

18 

.36511 

86 

.35908 

19 

.36530 

87 

.35927 

20 

.36549 

88 

.35946 

21 

.36568 

89 

.35965 

22 

.36586 

90 

.35984 

23 

.36605 

91 

.36003 

24 

.36624 

92 

.36021 

25     .36642 

93 

.36040 

26 

.36661 

94 

.36059 

27 

.36680 

109 


Bar. 
Height. 

Log. 

Bar. 
Height. 

Log. 

2328 

3.36698 

2361 

3.37310 

29 

.36717 

62 

.37328 

30 

.36736 

63 

.37346 

31 

.36754 

64 

.37365 

32 

.36773 

65 

.37383 

33 

.  36791 

66 

=37401 

34 

.36810 

67 

.37420 

35 

.36829 

68 

.37438 

36 

.36847 

69 

.37457 

37 

.36866 

70 

.37475 

38 

.35884 

71 

.37493 

39 

.36903 

72 

.37511 

40 

.36922 

73 

.37530 

41     .38940 

74 

.37548 

42 

.36959 

75 

.37566 

43 

.36977 

76 

.37585 

44 

.36996 

77     .37603 

'  45 

.37014 

78 

.37621 

46 

.37033 

79 

.37639 

47 

.37051 

80 

.37658 

48 

.37070 

81 

,37670 

49 

.37088 

82     .37694 

50 

.37107 

83 

37712 

51 

.37125 

84 

.37731 

52 

.37144 

85 

.37749 

53 

.37162 

86 

.37767 

54 

.37181 

87 

.37785 

55 

.37199 

88 

.37803 

56 

.37218 

89 

.37822 

57 

.37236 

90 

.37840 

58 

.37254 

91 

.37858 

59 

.37273 

92 

.37876 

60 

.37291 

1 

93 

.37894 

110 


Bar. 
Height. 

Log. 

Bar. 
Height. 

Log. 

2394 

3.37912 

2427 

3.38507 

95 

.37931 

28 

.38525 

96 

.37949 

29 

.38543 

97 

.37967 

30 

.38561 

98 

.37985 

31 

.38579 

99 

.38003 

32 

.38596 

2400 

.38021 

33 

.38614 

01 

.38039 

34 

.38632 

02 

.38057 

35 

.38650 

03 

.38075 

36 

.38668 

04 

.38093 

37 

.38686 

05 

.38112 

38 

.38703 

06 

.38130 

39 

.38721 

07 

.38148 

40 

.38739 

08 

.38166 

41 

.38757 

09 

.38184 

42 

.38775 

10 

.38202 

43 

.38792 

11 

.38220 

44 

.38810 

12 

.38238 

45 

.38828 

13 

.38256 

46 

.38846 

14 

.38274 

47 

.38863 

15 

.38292 

48 

.38881 

16 

.38310 

49 

.38899 

17 

38328 

50 

.38917 

18 

.38346 

51 

.38934 

19 

.38364 

52 

.38952 

20 

.38382 

53 

.38970 

21 

.38399 

54 

.38987 

22 

.38417 

55 

.39005 

23 

.38435 

56 

.39023 

24 

.38453 

57 

39041 

25 

.  38471 

58 

.39058 

26 

.38489 

59 

.39076 

Ill 


Bar. 
Height.  1 

Bar. 

Height. 

2460    3.39094 

2493    3.39672 

61     .39111 

94     .39690 

63     .39129 

95     .39707 

63 

.39146 

96     .39724 

64 

.39164 

97     .39742 

65 

.39182 

98     .39759 

06 

.39199 

99     .39777 

67 

.39217 

2500 

.39794 

68 

.39235 

01 

.39811 

69 

.39252 

02 

.39829 

70 

.39270 

03 

.39846 

71 

.39287 

04 

.39863 

72 

.39305 

05 

.39881 

73 

.39322 

06 

.39898 

74 

.39340 

07 

.39915 

75 

.39358 

08 

.39933 

76 

.39375 

09 

.39950 

77 

.39393 

10 

.39967 

78 

.39410 

11 

.39985 

79 

.39428 

12 

40002 

80 

.39445 

13 

.40019 

81 

.39463 

14 

.40037 

82 

.39480 

15 

.40054 

83 

.39498 

16 

.40071 

84 

.39515 

17 

.40088 

85  |   .39533 

18 

.40106 

86 

.39550 

19 

.40123 

87 

.39568 

20 

.40140 

88 

.39585 

21 

.40157 

89 

.39602 

22 

.40175 

90 

.39620 

23 

.40192 

91 

.39637 

24 

.40209 

92 

.39655 

25 

.40226 

112 


1 

Bar. 

Height.  1 

Bar. 
Height. 

Log. 

2526    3.40243 

255J 

3.40807 

27     .40261 

60 

.40824 

28     .40278 

61 

.40841 

29 

.40295 

62 

.40858 

an 

.40312 

63 

.40875 

31 

.40329 

64     .40892 

32 

.40346 

65    .401)0:; 

33 

.40364 

66     .40926 

34 

.40381 

67     .40943 

35 

.40398 

68     .40960 

36 

.40415 

69     .40976 

37 

.40432 

70     .40993 

38 

.40449 

71     .41010 

39 

.40466 

72     .41027 

40 

.40483 

73 

.41044 

41 

.40500 

74 

.41061 

42 

.40518 

75 

.41078 

& 

.40535 

76 

.41095 

44 

.40552 

77 

.41111 

45 

.40569 

78 

.41128 

46 

.40586 

79 

.4114') 

47 

.40603 

80     .41162 

48 

.40620 

81     .41179 

49 

.40637 

82     .41196 

50 

.40654 

83     .41212 

51 

.40671 

84 

.41229 

52 

.40688 

85     .41246 

53 

.40705 

86     .41263 

54 

.40722 

87     .41280 

5) 

•40739 

88     .41296 

56 

.40756 

89     41313 

57 

.40773 

90 

.41330 

58 

.40790 

91 

.41347 

113 


Bar. 

Height. 

Log. 

Bar. 

Height. 

Log. 

2592 

3.41364 

2625 

3.41913 

93 

.41880 

26 

.41929 

94 

.41397 

27 

.41946 

95 

.41414 

28 

.41963: 

96 

.41430 

29 

.4197$ 

97 

.41447 

30 

.41996- 

98 

.41464 

31 

.42012 

99 

.41481 

32 

.42029' 

2600 

.41497 

33 

.42045. 

01 

.41514 

34 

.420621 

02 

.41531 

35 

.4207$ 

03 

.41547 

36 

.42095 

04 

41564 

37 

.42111 

05 

.41581 

38 

.42127 

06 

.41597 

89 

.42144 

07 

.41614 

40 

.42160 

08 

.41631 

41 

.42177 

09 

41647 

42 

.42193: 

10 

.41664 

43 

.42210 

11 

.41681 

44 

.42226 

12 

.41697 

45 

.42243: 

13 

.41713 

46 

.42259 

14 

.41731 

47 

.42275 

15 

.41747 

46 

.42292 

16 

.41764 

49 

42308 

17 

,41781 

50 

.42:',25 

18 

.41797 

51 

42341 

19 

.41814 

52 

.42357 

20 

.41831 

53 

,  42374 

21 

.41847 

54 

.42390 

22 

.41863 

55 

.42406 

23 

.41880 

56 

.  42423 

24 

41896 

57 

42439 

114 


"Rar 

Height.    L°S' 

I  )<  1  1  . 

Height. 

Log. 

2658 

3.42455 

2691 

3.42991 

59 

.42472 

92 

43008 

60 

.42488 

93 

.43024  - 

61 

.42504 

94 

.43040 

62 

.42521 

95 

.43056 

63 

.42537 

96 

.43072 

64 

.42553 

97 

.43088 

65 

.42570 

98 

.43104 

66 

.42586 

99 

.43120 

67 

.42602 

2700 

.43136 

68 

.42619 

01 

.43152 

69 

.42635 

02 

.43169 

70 

.42651 

03 

.43185 

71 

.42667 

04 

.43201 

72 

.42684 

05 

.43217 

73 

.42700 

06 

.43233 

74 

.42716 

07 

.43249 

75 

.42732 

08 

.43265 

76 

.42749 

09 

.43281 

77 

.42765 

10 

.43297 

78 

.42781 

11 

.43313 

79 

.42797 

12 

.43329 

80 

,42813 

13 

.43345 

81 

.42830 

14 

.43361 

82 

.42846 

15 

.43377 

83 

,42862 

16 

.43393 

84 

42878 

17 

.43409 

85 

.42894 

18 

.43425 

86 

.42911 

19 

.43441 

87 

.42927 

20 

.43457 

88 

.42943 

21 

.43473 

89 

.42959 

22 

.43489 

90 

.42975 

23 

.43505 

115 


Bar. 
Height. 

Log. 

Bar. 
Height. 

Log. 

2724 

3.48521 

2757 

3.44044 

25 

.43537 

58 

.44059 

26 

.43553 

59 

.44075 

27 

.43569 

60 

.44091 

28 

.43584 

61 

.44107 

29 

.43600 

62 

.44122 

30 

.43616 

63 

.44138 

31 

.43632 

64 

.44154 

32 

.43648 

65 

.44170 

33 

.43664 

66 

.44185 

34 

.43680 

67 

.44201 

35 

.43696 

68 

.44217 

36 

.43712 

69 

.44232 

37 

.43727 

70 

.44248 

38 

.43743 

71 

.44264 

39 

.43759 

72 

.44279 

40 

.43775 

73 

.41295 

41 

.48791 

74 

.44311 

42 

.43807 

75 

.44326 

43 

.43823 

76 

.44342 

44 

.43838 

77 

.44358 

45 

.43854 

78 

.44373 

46 

.43870 

79 

.44389 

47 

.43886 

80 

.44404 

48 

.43902 

81 

.44420 

49 

.43917 

82 

.44436 

50 

.43933 

83 

.44451 

51 

.43949 

84 

.44467 

52 

.43965 

85 

.44483 

53 

,43981 

86 

.44498 

54 

.43996 

87 

.44514 

55 

.44012 

88 

.44529 

56 

.44028 

89 

.44545 

1 

116 


Bar. 
Height. 

Log. 

Bar. 
Height. 

Log. 

2790 

3.44560 

2823 

3.45071 

91 

.44576 

24 

.45086 

92 

.44592 

25 

.45102 

93 

.44607 

26 

.45117 

94 

.44623 

27 

.45133 

95 

.44638 

28 

.45148 

96 

.44654 

29 

.45163 

97 

.44669 

30 

.45179 

98 

.44685 

31 

.45194 

99 

.44700 

32 

.45209 

2800 

.44716 

33 

.45225 

01 

.44731 

34 

.45240 

02 

.44747 

35 

.45255 

03 

.44762 

36 

.45271 

€4 

.44778 

37 

.45287 

€5 

.44793 

38 

.45301 

06 

.44809 

39 

.45817 

07 

.44824 

40 

.45332 

08 

.44840 

41 

.45347 

09 

.44855 

42 

.45362 

10 

.44871 

43 

.45378 

11 

.44886 

44 

.45393 

12 

.44902 

45 

.45408 

13 

.44917 

46     .45423 

14 

.44932 

47     .45439 

15 

.44948 

48  |   .45454 

16 

.44963 

49     .45469 

17 

.44979 

50  i   .45484 

18 

.44994 

51     .45500 

19 

.45010 

52     .45515 

20 

.45025 

53 

.45530 

21 

.45040 

54 

.45545 

22 

.45056 

55 

.45561 

117 


Bar. 
Height. 

Log. 

Bar. 
Height. 

Log. 

2856 

3.45576 

2889 

3.46075 

57 

.45591 

90 

.46090 

58 

.45606 

91 

.46105 

59 

.45621 

92 

.46120 

60 

.45637 

93 

.46135 

61 

.45652 

94 

.46150 

62 

.45667 

95 

.46165 

63 

.45682 

96 

.46180 

64 

.45698 

97 

.46195 

65 

.45712 

98 

.46210 

66 

.45728 

99 

.46225 

67 

.45743 

2900 

.46240 

68 

.45758 

01 

.46255 

69 

.45773 

02 

.46270 

70 

.45788 

03 

.46285 

71 

.45803 

04 

.46300 

72 

.45818 

05 

.46315 

73 

.45834 

06 

.46330 

74 

.45849 

07 

.46344 

75 

.45864 

08 

.46859 

76 

.45879 

09 

.46374 

77 

.45894 

10 

.46389 

78 

.45909 

11 

.46404 

79 

.45924 

12 

.46419 

80 

.45989 

13 

.46434 

81 

.45954 

14 

.46449 

82 

.45969 

15 

.46464 

83 

.45984 

16 

.46479 

84 

.46000 

17 

.46494 

85 

.46015 

18 

.46509 

86 

.46030 

19 

.46523 

87 

.46045 

20 

.46538 

88 

46060 

21 

.46553 

118 


i 

Bar. 
Height. 

Log. 

Bar. 
Height. 

Log. 

2922 

3.46568      2955 

3.47056 

23 

.46583        56 

.47070 

24 

.46598 

57 

.47085 

25 

.46613 

58 

.47100 

26 

.466^7 

59 

.47114 

27 

.46642 

60 

.47129 

28 

.46657 

61 

.47144 

29 

.46672 

62 

.47159 

30 

.46687 

63 

.47176 

31 

.46702 

64 

.47188 

32 

.46716 

65 

.47202 

33 

.46731 

66 

.47217 

34 

.46746 

67 

.47232 

35 

.46761 

68 

.47246 

36 

.46776 

69 

.47261 

37* 

.46790 

70 

.47276 

38 

.46805 

71 

.47290 

39 

.46820 

72 

.47305 

40 

.46835 

73 

.47319 

41 

.46849 

74 

.47334 

42 

.46864 

75 

.47349 

43 

.46879 

76 

.47363 

44 

.46894 

77 

.47378 

45 

.46909 

78 

.47392 

46 

.46923 

79 

.47407 

47 

.46938 

80 

.47422 

48 

.46953 

81 

.47436 

49 

.46967 

82 

.47451 

50 

.46982 

83 

.47465 

51 

.46997 

84 

.47480 

52 

.47012 

85 

.47494 

53 

.47026 

86 

.47509, 

54 

.47041 

87 

.47524^ 

119 


Hefght.    L°S- 

Bar. 
Height. 

Log. 

2988    3.47538 

3021 

3.48015 

89     .47553 

22 

.48030 

90     .47567 

23 

.48044 

91     47582 

24 

.48058 

92 

.47596 

25 

.48073' 

93 

47611 

26 

.48087 

04 

.47625 

27 

.48101 

95 

.  47640 

28 

.48116 

96 

.47654 

29 

.48130 

97 

.47669 

30 

.48144 

98 

.47683 

31 

.48159 

99     .47698 

32 

.48173 

3000     .47712 

33 

.48187 

01 

.47727 

34 

.48202 

03 

47741 

35 

.48216 

03 

47755 

36 

.48230 

04 

.  47770 

37 

.48244 

05 

.  47784 

38 

.48259 

06 

.47799 

39 

.48273 

07 

.47813 

40 

.48287 

08 

.47828 

41 

.48302 

09 

.  47842 

42 

.48316 

10 

.  47857 

43 

.48330 

11 

.47871 

44 

.48344 

12 

.47886 

45 

.48359 

13 

.47900 

46 

.48373 

14 

.47914 

47 

.48387 

15 

.47929 

48 

.48402 

16 

.47943 

49 

,48416 

17 

.47958 

50 

48430 

18 

.47972 

51 

,48444 

19 

47986 

52 

.48458 

20 

,48001 

53 

.48473 

120 


Bar. 
Height. 

Log. 

Bar. 
Height.  | 

Log. 

3054 

3.48487 

3078 

3.48827 

55 

.48501 

79 

.48841 

56 

.48515 

80 

.48855 

57 

.48530 

81 

.48869 

58 

.48544 

82 

.48883: 

59 

.48558 

83 

48897 

60 

.48572 

84 

.48911 

61 

.48586 

85 

.48926 

62 

.48601 

86 

.48940 

63 

.48615 

87 

.48954 

64 

.48629 

88 

.4896$ 

65 

.48643 

89 

.  48982 

66 

.48657 

90 

.48996 

67 

.48671 

91 

.49010 

68 

.48686 

92 

.49024 

69 

.48700 

93 

49038 

70 

.48714 

94  1 

.  49052 

71 

.48728 

95 

.49066 

72 

.48742 

96 

.  49080 

73 

.48756 

97 

.49094 

74 

.48770 

98 

.49108 

75 

.48785 

99 

.49122 

76 

.48799 

3100 

.49136 

77 

.48813 

121 


TABLE  III. 

BAROMETRIC    READINGS    IN    MILLIMETERS. 

ALTITUDES    IN    METERS. 

This  is  from  Radau's  table.     The  formula 
for  calculation  of  difference  of  altitude  of  two 

stations  is  D=(h—h')  11+  -    +    I  in  which  D 

is  the  difference  of  height  in  meters,  h  and  hf 
arc  barometer  readings  in  millimeters  and  I  and 
t'  are  the  temperatures  in  centigrade  degrees. 


Mill. 

Meters.    j|  Mill. 

Meters. 

Mill. 

Meters. 

500 

3365.4 

519 

3067  4 

538 

2780.0 

501 

3349.4 

520 

3052  0 

539 

2765.2 

502 

3333.5 

521 

3036.6 

540 

2750.4 

503 

3317.6 

\  522 

3021  3 

541 

2735.6 

504 

3301  7 

523 

3006  0 

542 

2720.9 

505 

3285.9 

524 

2990  7 

543 

2706.1 

506 

3270.1 

525 

2975.5 

544 

2691.4 

507  |  3254.3 

526 

2960.3 

545 

2676.8 

508 

3238.5 

527 

2945  1 

546 

2662.1 

509 

3222.8 

528 

2930  0 

547 

2647.5 

510 

3207  1 

529 

2914  9     |  548 

2632.9 

511 

3191.5 

530 

2899  8 

549 

2618.3 

512 

3175.9 

531 

2884.7 

550 

2603.8 

513 

3160.3 

532 

2869.7 

551 

2589.3 

514 

3144.7 

533 

2854.7 

552 

2574.8 

515 

3129.2 

534 

2839.7 

553 

2560.3 

516 

3113.7 

535 

2824.7 

554 

2545  9 

517 

3098.2 

536 

2809.8 

555 

2531.5 

518 

3082.8 

537 

2794.9 

556 

2517.1 

i 

122 


Mill. 

Meters. 

Mill. 

Meters. 

Mill. 

Meters. 

557 

2502.7 

591 

2029  4 

625 

1582.6 

558 

2488.4 

592 

2015  9 

626 

1569.8 

559 

2474  1 

593 

2002  4 

627 

1557.1 

560 

2459.8 

594 

1989.0 

628 

1544.4 

561 

2445.6 

595 

1975.5 

029 

1531.7 

562 

2431  4 

596 

1962  1 

630 

1519.0 

563 

2417.2 

597 

1948.7 

631 

1506.3 

564 

2403.0 

598 

1935.4 

632 

1493.7 

565 

2388.8  ! 

599 

1922.0 

633 

1481.0 

566 

2374.7 

600 

1Q08.7 

034 

1468.4 

567 

2360.6 

601 

1895.4 

635 

1455.8 

568 

2346  5 

602 

1882.1 

636 

1443.3 

5(59 

2332.5 

603 

1868.8 

637 

1430.7 

570 

2318.4 

604 

1855.6 

638 

1418.2 

571 

2304  4 

605 

1842.4 

639 

1405.7' 

572 

2290.4 

606 

1829.2 

640 

1393.2 

573 

2276.5 

607 

1816.0 

641 

1380.7 

574 

2262.6 

608 

1802.9 

642 

1368.3 

575 

2248.7 

609 

1789.8 

643 

1355.8 

576 

2234.8 

610 

1776.7 

644 

1343.4 

577 

2220.9 

611 

1763.6 

645 

1331.0 

578 

2207.1 

612 

1750.5 

646 

1318.7 

579 

2193.3 

613  1737.5 

647 

1306.3 

580 

2179  5 

614  1724.4 

648 

1294.0 

581 

2165.7 

615  1711.4 

649 

1281.7 

582 

2152.0 

616  1698.5 

650 

1269.4 

583 

2138.3 

617 

1685.5 

651 

1257.1 

584 

2124.6 

618 

1672.6 

652 

1244.8 

585 

2110.9 

619 

1659.7 

653 

1232.6 

586 

2097.3 

620 

1646.8 

654 

1220.4 

587 

2083.7 

621 

1683.9 

655 

1208.2 

588 

2070.1 

622 

1621.0 

656 

1196.0 

589 

"2056.5 

623 

1608.2 

657 

1183.8 

590 

2042.9 

624 

1595.4 

658 

1171  7 

123 


Mill. 

Meters. 

Mill. 

Meters. 

Mill 

Meters. 

659 

1159.5 

693 

757.8 

727       375.4 

6GO 

1147.4 

694 

746.3 

728  !     364.4 

661 

1135.3 

695 

734.8 

729 

353.5 

662 

1123.3 

696 

723.3 

730 

842.5 

663 

1111.3 

697 

711.9 

731 

831.6 

664 

1099.2 

698 

700.4 

732 

820.7 

665 

10b7.2 

699 

689.0 

733 

309.8 

666 

1075.2 

700 

677.6 

734 

298.9 

667 

1063.2 

701 

666.2 

735 

288.0 

668 

1051  2 

702 

654.8 

736 

277.2 

669 

1039.3 

703 

643.4 

737 

266.3 

670 

1027.3 

704 

632.1 

738 

255.5 

671 

1015.4 

705 

620.7 

739 

244.7 

672 

1003.5 

706 

609.4 

740 

233.9 

673 

991.7 

707 

598.1 

741 

223.1 

674 

979.8 

708 

586.8 

742 

212.3 

675 

968.0 

709 

575.6 

743 

201.6 

676 

956.1 

710 

564.3 

744 

190.8 

677 

944.3 

711 

553.1 

745 

180.1 

678 

932.6 

712 

541  8 

746 

169.4 

679 

920.8 

713 

530.6 

747 

158.7 

680 

909.0 

714 

519.5 

748 

148.0 

681 

897.3 

715 

508.3 

749 

137.4 

682 

885.6 

716 

497.1 

750 

126.7- 

683 

873.9 

717       486.0    ! 

751 

116.1 

684 

862.2 

718 

474.8    i 

752 

105.5 

685 

850.5 

719 

463.7    j 

753 

94.9 

686 

838.9 

720 

452.6 

754 

84.3 

687 

827.3 

721 

441.6    ! 

755 

73.7 

688 

815.6 

722 

430.5 

756 

63.1 

689 

8C4.0 

723 

419.4 

757 

52.6 

690 

792.5 

724 

40S.4 

758 

42.0 

691 

780.9 

725 

397.4 

759 

31.5 

692 

769.3 

726 

386.4 

760 

21.0 

124 


Mill. 

Meters. 

Mill. 

Meters. 

Mill. 

Meters. 

761. 

10.5 

768 

-  62.6 

775 

-135.0 

762 

0  0 

769 

-  73.0 

776 

-145  3 

763 

-10  5 

770 

-  83.4 

777 

-155  6 

764 

-20  9 

771 

-  93.7 

778 

-165.9 

765 

-31  4 

772 

-104  1 

779 

-176.1 

766 

-41  8 

773 

-114  4 

780 

-186.4 

767 

-52.2 

774 

-124.7 

125 

In  comparing  the  Aneroid  with  a  Mercurial 
Barometer,  correct  the  latter  by  the  following 
table,  subtracting  the  corrections. 

TABLE  IV. 

Reduction  of  Mercurial  Column  to  32°  Fahr. 
Brass  scale  to  barometer  correct  at  62°  Fahr. 


Temp. 

30" 

25" 

20" 

32 

.009 

.008 

.006 

35 

.017 

.015 

.012 

40 

.031 

.026 

.021 

45 

.044 

.037 

.030 

50 

.058 

.048 

.038 

55 

.071 

.059 

.047 

60 

..084 

.070 

.056 

65 

.098 

.082 

.065 

70 

.111 

.093 

.074 

75 

125 

.104 

.083 

80 

.138 

.115 

.092 

85 

.151 

.126 

.101 

90 

.164 

.137 

.110 

95 

.178 

.148 

.118 

100 

.191 

.159 

.127 

126 


TABLE  Y. 

BAROMETRIC  PRESSURES    CORRESPONDING  TO 
BOILING  WATER      TEMPERATURES. 


Whole  Deg. 
.0 

Tenths  of  each  Degree. 

.2 

s  -4 

.6 

.8 

in. 

in. 

in 

in.     in. 

183 

16.317 

16  389 

16.461 

16.533  116.605 

184 

16  618 

16  752 

16.826 

16.900 

16.974 

185 

17  048 

17  122 

17.197 

17.272 

17.348 

186 

17  423 

17  499 

17.575 

17.652 

17.729 

187 

17  806 

17.883 

17.961 

18.039 

18.117 

188 

18  195 

18.274 

18.353 

18.432 

18.512 

189 

18  592 

18.672 

18.753 

18.833 

18.914 

190 

18  996 

19.077 

19.159 

19.241 

19.324 

191 

19  407 

19.490 

19.573 

19.657 

19.741 

192 

19  825 

19.910 

19.995 

20.080 

20.166 

193 

20  251 

20.338 

20.424 

20  511 

20.598 

194  '20  685 

20.773 

20.861 

20  949 

21.038 

195 

21.126 

21.216 

21.305 

21.895 

21.485 

196 

21  .  576 

21  .  666 

21.758 

21.849 

21.941 

197 

22  .  033 

22.125 

22.218 

22.311 

22.404 

198 

22  498 

22  592 

22.686 

22.781 

22.876 

199 

22  971 

23  067 

23.163 

23.259 

23.356 

200 

23  .  453 

23  550 

23.648 

23.746 

23.845 

201 

23  .  943 

24  042 

24.142 

24.241 

24.341 

202 

24  442 

24.542 

24.644 

24.745 

24.847 

203 

24  949 

25  051 

25.154 

25.257 

25  361 

204  25  465 

25  569 

25  674 

25.779 

25.884 

205 

25  990 

26  096 

26.202 

26.309 

26.416 

206 

26  523 

26  .  631 

26.740 

26.848 

26.957 

207 

27  066 

27.176 

27.286 

27.397 

27.507 

208 

27.618 

27.730 

27.842 

27.954 

28.067 

209 

28  180 

28.293 

28.407 

28.521 

28.636 

210 

28.751 

28.866 

28.982 

29.098 

29.215 

211 

29.331 

29.449 

29.566 

29.684 

29  803 

212 

29.922 

30.041 

30.161 

30.281 

30.401 

•»*  Any  book  in  this  Catalogue  sent  free  by  mail  on  receipt  o/ 

VALUABLE 

SCIENTIFIC    BOOKS 


PUBLISHED   BY 


D.  VAN  NOSTRAND  COMPANY, 

23  MURRAY  STREET  AND  27  WARREN  STREET,  N.  Y. 


ADAMS  (J.  W.)  Sewers  and  Drains  for  Populous  Districts. 
Embracing  Rules  and  Formulas  lor  the  dimensions  and 
construction  of  works  of  Sanitary  Engineers.  Second  edi- 
tion. 8vo,  cloth $2  50 

ALEXANDER  (J.  H.)  Universal  Dictionary  of  Weights  and 
Measures,  Ancient  and  Modern,  reduced  to  the  standards 
of  the  United  States  of  America.  New  edition,  enlarged. 
8vo,  cloth 350 

ATWOOD  (GEO.)    Practical  Blow-Pipe  Assaying.  I2mo,  cloth, 

illustrated 2  OO 

AUCHINCLOSS  (W.  S.)  Link  and  Valve  Motions  Simplified. 
Illustrated  with  37  wood-cuts  and  21  lithographic  plates, 
together  with  a  Travel  Scale  and  numerous  useful  tables. 
8vo,  cloth 300 

AXONf  (W.  E.  A.)  The  Mechanic's  Friend  :  a  Collection  of  Re- 
ceipts  and  Practical  Suggestions  Relating  to  Aquaria- 
Bronzing — Cements — Drawing — Dyes— Electricity — Gilding 
—Glass-working  —  Glues  —  Horology  —  Lacquers  -Locomo- 
tives— Magnetism— Metal-working  Modelling  —  Photogra- 
phy— Pyrotec^ny — Railways — Solders — Steam-Engine — Tel- 
egraphy— Taxiuermv— Varnishes— Waterproofing,  and  Mis- 
cellaneous Tools,  Instruments,  Machines,  and  Processes 
connected  with  tne  Chemical  and  Mechanic  Arts.  With  nu- 
merous diagrams  and  wood-cuts.  Fancy  cloth  .....  ..  I  50 

&ACON  (F.  W  )  A  Treatise  on  the  Richards  Steam-Engjne 
Indicator,  with  directions  for  its  use.  By  Charles  T.  Por- 
ter. Revised,  with  notes  and  large  additions  as  developed 
by  American  practice ;  with  an  appendix  containing  useful 
formulae  and  rules  for  engineers.  Illustrated.  Third  edi- 
tion. i2mo,  cloth: ......  £  oo 


2  D.    VAN    NOSTRAND  S   PUBLICATIONS. 

BARBA  (J.)  The  Use  of  Steel  for  Constructive  Purposes  • 
Method  of  Working,  Applying,  and  Testing  Plates  and 
Brass.  With  a  Prelace  by  A.  L.  Holley,  C.E.  12010,  cloth.$i  50 

BARNES  (Lt.  Com.  J.  S..  U.  S.  N.)  Submarine  Warfare,  offen- 
sive and  defensive,  including  a  discussion  of  the  offensive 
Torpedo  System,  its  effects  upon  Iron-Clad  Ship  Systems 
and  influence  upon  future  naval  wars.  With  twenty  litho- 
graphic plates  and  many  wood-cuts.  8vo,  cloth 5  oo 

BE1LS  TEIN   (F.)     An  Introduction  to  Qualitative  Chemical 

Analysis,  translated  by  I.  J.  Osbun.     i2mo,  cloth 75 

BENET  (Gen.  S.  V.,  U.  S.  A.)  Electro-Ballistic  Machines,  and 
the  Schultz  Chronoscope.  Illustrated.  Second  edition,  410, 
cloth  300 

BLAKE  (W.  P.)  Report  upon  the  Precious  Metals :  Being  Sta- 
tisiic.il  Notices  of  the  principal  Gold  and  Silver  producing 
regions  of  the  World,  represented  at  the  Paris  Universal 
Exposition.  8vo,  cloth 200 

— —  Ceramic  Art.  A  Report  on  Pottery,  Porcelain,  Tiles, 

Terra  Cotta,  and  Brick.  8vo,  cloth 2  oo 

BOW  (R.  H.)  A  Treatise  on  Bracing,  with  its  application  to 
Bridges  and  other  Structures  of  Wood  or  Iron.  156  illustra- 
tions. 8vo,  cloth i  «;o 

BOW  SLR  (Prof.  E.  A.)  An  Elementary  Treatise  on  Analytic 
Geometry,  embracing  Plane  Geometry,  and  an  Introduc- 
tion to  Geometry  of  three  Dimensions.  I2mo,  cloth I  75 

-  An  Elementary  Treatise  on  the  Differential  and  Integral 

Calculus.  With  numerous  examples.  I2mo,  cloth 225 

BURGH  (N  P.)  Modern  Marine  Engineering,  applied  to  Pad- 
dle and  Screw  Propulsion.  Consisting  of  36  colored  plates, 
259  practical  wood-cut  illustrations,  and  403  pages  of  de- 
scriptive matter,  the  whole  being  an  exposition  of  the  pre- 
sent practice  of  Tames  Watt  &  Co.,  J.  &  G.  Rennie,  R.  Na- 
pier &  Sons,  and  other  celebrated  firms.  Thick  410  vol., 

cloth 3 10  oo 

Hail  morocco , 15  oo 

BUR  f  (W.  A.)  Key  to  the  Solar  Compass,  and  Surveyor's  Com- 
panion ;  comprising  all  the  rules  necessary  for  use  in  the 
held :  also  description  of  the  Linear  Surveys  and  Public 
Land  Astern  of  the  United  States,  Notes  on  the  Karome- 
ter,  -.tgestions  for  an  outfit  for  a  survey  of  four  months, 
etc.  .second  edition.  Pocket-book  form,  tuck 2  50 

BUTLER  (Capt.  J.  S.,  U.  S.  A.)  Projectiles  and  Rifled  Cannon. 
A  Critical  Discussion  of  the  Principal  Systems  of  Rifling 
and  Projectiles,  with  Practical  Suggestions  for  their  Im- 
provement, as  embraced  in  a  Report  to  the  Chief  of  Ord- 
nance, U.  S.  A.  s6plates  410,  cloth 6  oo 


D.    VAN    NOSTRAND7S   PUBLICATIONS.  3 

CAI N  (Prof.  WM  )     A  Practical  Treatise  on  Voussoir  and  Solid 

and  Braced  Arches.     i6mo,  cloth  extra  $j  75 

CALDWELL  (Prof.  GEO.  C.)  and  BRENEMAN  (Prof.  A.  A.) 
Manual  of  Introductory  Chemical  Practice,  for  the  use  of 
Students  in  Co  leges  and  Normal  and  High  Schools.  Third 
edition,  revised  and  corrected.  8vo,  cloth,  illustrated.  New 
and  enlarged  edition I  50 

CAMPIN  (FRANCIS).    On  the  Construction  of  Iron  Roofs.  8vo, 

with  plates,  cloth . .    . .  2  oo 

CHAUVENET(Prof.  W.)  New  method  of  correcting  Lunar 
Distances,  and  improved  method  of  finding  the  error  and 
rate  of  a  chronometer,  by  equal  altitudes.  8vo,  cloth 200 

CHURCH  (JOHN  A.)     Notes  of  a  Metallurgical  Journey  in 

Europe.     8vo,  cloth 2  oo 

CLARK  (D.  KINNEAR,  C.E.)  Fuel:  Its  Combustion  and 
Economy,  consisting  of  Abridgments  of  Treatise  on  the 
Combustion  of  Coal  and  the  Prevention  of  Smoke,  by  C. 
W.  Williams ;  and  the  Economy  of  Fuel,  by  T  S  Pri- 
deaux.  With  extensive  additions  on  recent  practice  in  the 
Combustion  and  Economy  of  Fuel :  Coal,  Coke,  Wood, 
Peat,  Petroleum,  etc.  I2mo,  cloth I  50 

A  Manual  of  Rules,  Tables,  and  Data  for  Mechanical 

Engineers.  Hased  on  the  most  recent  investigations.     Illus- 
trated with  numerous  diagrams.     1,012  pages.'  8vo,  cloth...  7  50 
Half  morocco 10  oo 

CLARK  (Lt.  LEWIS,  U.  S.  N  )  Theoretical  Navigation  and 
Nautical  Astronomy,  illustrated  with  41  wood-cuts.  8vo, 
cloth I  50 

CLARKE  (T.  C.)  Description  of  the  Iron  Railway  Bridge  oyf  r 
the  Mississippi  River  at  Quincy,  Illinois.  Illustrated  with 
21  lithographed  plans.  410,  cloth 7  50 

CLEVENGERfS.  R.)  A  Treatise  on  the  Method  of  Govern- 
ment Survexing,  as  prescribed  by  the  U  S.  Congress  and 
Commissioner  of  the  General  Land  Office,  with  complete 
Mathematical,  Astronomical,  and  Practical  Instructions  for 
the  use  of  the  United  States  Surveyors  in  the  field.  i6mo, 
morocco  2  50 

COFFIN  (Prof  J.  H.  C  )  Navigation  and  Nautical  Astrono- 
my. Prepared  for  the  use  of  the  U.  S.  Naval  Academy. 
Sixth  edition.  52  wood-cut  illustrations.  I2mo,  cloth.. 3  50 

COLBURN   (ZERAH).     The  Gas-Works  of   London.     I2mo, 

boards 60 

COLLINS  (JAS.  E)    The  Private  Book  of  Useful  Alloys  and 

Memoranda  for  Goldsmiths,  Jewellers,  etc.     i8mo,  cloth...      50 


4  D.  VAN  NOSTRAND'S  PUBLICATIONS. 

CORNWALL  (Prof.  H.  B.)  Manual  of  Blow  Pipe  Analysis, 
Qualitative  and  Quantitative,  with  a  Complete  System  01 
Descriptive  Mineralogy.  8vo,  cloth,  with  many  illustra- 
tions. N.  Y.,  1882 $250 

CRAIG  (B.  F  )  Weights  and  Measures.  An  account  of  the 
Decimal  System,  with  Tables  of  Conversion  for  Commer- 
cial and  Scientific  Uses.  Square  32mo,  limp  cloth 50 

CRAIG  (Prof.  THOS.)    Elements  of  the  Mathematical  Theory 

of  Fluid  Motion.     i6mo,  cloth 125 

DAVIS  (C.  B.I  and  RAE  (F.  B.)  Hand-Book  of  Electrical  Dia- 
grams and  Connections.  Illustrated  with  32  full-page  illus- 
trations. Second  edition.  Oblong  8vo,  cloth  extra  .......  too 

DIED  RICH  (JOHN).  The  Theory  of  Strains  :  a  Compendium 
lor  the  Calculation  and  Construction  of  Bridges,  Roofs,  and 
Cranes  Illustrated  by  numerous  plates  and  diagrams. 
8vo,  cloth 5  00 

DIXON  (D.  B.)  The  Machinist's  and  Steam-Engineer's  Prac- 
tical Calculator.  A  Compilation  of  useful  Rules,  and  Prob- 
lems Arithmetically  Solved,  together  with  General  Informa- 
tion applicable  to  Shop-Tools,  Mill-Gearing,  Pulleys  and 
Shafts,  Steam-Boilers  and  Engines.  Embracing  Valuable 
Tables,  and  Instruction  in  Screw-cutting,  Valve  and  Link 
Motion,  etc.  i6mo,  full  morocco,  pocket  form  ...(In  press) 

DODD  (GEO.)  Dictionary  of  Manufactures,  Mining,  Ma- 
chinery, and  the  Industrial  Arts.  I2mo,  cloth 150 

DOUGLASS 'Prof  S.  H.)  and  PRESCOTT  (Prof.  A  B.)  Qual- 
itative Chemical  Analysis.  A  Guide  in  the  Practical  Study 
of  Chemistry,  and  in  the  Work  of  Analysis.  Third  edition. 
8vo,  cloth 3  50 

DUBOIS  (A.  T.)    The  New  Method  of  Graphical  Statics.  With 

60  illustrations.    8vo,  cloth  i  150 

EASSIE  (P.  B.)  Wood  and  its  Uses.  A_  Hand-Book  for  the  use 
of  Contractors,  Builders,  Architects,  Engineers,  and  Tim- 
ber Merchants.  Upwards  of  250  illustrations.  8vo,  cloth,  i  50 

EDDY  (Prof.  H.  T.)  Researches  in  Graphical  Statics,  err'dac- 
ing  New  Constructions  in  Graphical  Statics,  a  New  General 
Method  in  Graphical  Statics,  and  the  Theory  of  Internal 
Stress  in  Graphical  Statics.  8vo,  cloth i  <y) 

ELIOT  (Prof.  C.  W  )  and  STOKER  (Prof.  F.  H.)  A  Compen- 
dious Manual  of  Qualitative  Chemical  Analysis  Revised 
with  the  co-operation  ol  the  authors.  By  Prof.  William  R. 
Nichols.  Illustrated.  I2mo,, cloth I  50 

ELLIOT  (Maj.  GEO.  H.,  U.  S.  R.)  European  Light-House 
Systems.  Being  a  Report  of  a  Tour  of  Inspection  made  in 
1873.  51  engravings  and  21  wood-cuts.  8vo,  cloth 5  oo 


D.  VAN  NOSTRAND'S  PUBLICATIONS.  5 

ENGINEERING  FACTS  AND  FIGURES.  An  Annual 
Register  of  Progress  in  Mechanical  Engineering  and  Con- 
struction for  the  years  1863-6.1-65-66-67-68.  Fully  illus- 
trated. 6  vols.  i8mo,  cloth  (each  volume  sold  separatel>), 
per  vol $2  50 

FANNING  (J.  T.)  A  Practical  Treatise  of  Water-Supply  En- 
gineering. Relating  to  the  Hydrology,  Hydrodynamics,  and 
Practical  Construction  ol  Water- \V  orks  in  North  America. 
Third  edition.  With  numerous  tables  and  180  illustra- 
tions, 650  pages .  8vo,  cloth 5  oo 

FISkE  (BRADLEY  A.,  U.S.  N.)    Electricity  in  Theory  and 

Practice.    8vo,  cloth , . . .  2  50 

FOSTER  (Gen.  J.  G.,  U.  S.  A.)  Submarine  Blasting  in  Boston 
Harbor,  Massachusetts.  Removal  ot  Tower  and  Corwin 
Rocks.  Illustrated  with  seven  plates.  410,  cloth 3  50 

FOYE  (Prof.  T.  C.)  Chemical  Problems.  With  brief  State- 
ments of  the  Principles  involved.  Second  edition,  revised 
and  enlarged.  i6mo,  boards 50 

FRANCIS  (JAS.  B.,  C  E.)  Lowell  Hydraulic  Experiments: 
Being  a  selection  from  Experiments  on  Hydraulic  Motors, 
on  the  Flow  of  Water  over  Weirs,  in  Open  Canals  of  Uni- 
form Rectangular  Section,  and  through  submerged  Orifices 
and  diverging  Tubes.  Made  at  Lowell,  Massachusetts. 
Fourth  edition,  revised  and  enlarged,  with  many  new  ex- 
periments, and  illustrated  with  twenty-three  copperplate 
engravings.  410,  cloth = , 15  oo 

FREE-HAND  DRAWING.  A  Guide  to  Ornamental  Figure 
and  Landscape  Drawing.  By  an  Art  Studeiu.  l8mo, 
boards go 

GILLMORE  (Gen.  Q.  A.)  Treatise  on  Limes,  Hydraulic  Ce- 
ments, and  Mortars.  Papers  on  Practical  Engineering,  U. 
S.  Engineer  Department,  No.  9,  containing  Reports  or 
numerous  Experiments  conducced  in  New  York  City  during 
the  years  1858  to  1861,  inclusive.  With  numerous  illustra- 
tions. 8vo,  cloth 4  OO 

Practical  Treatise  on  the  Construction  of  Roads,  Streets, 

and  Pavements.     With  70  illustrations.     I2mo,  cloth 2  OO 

Report  on  Strength  of  the  Building  Stones  in  the  United 

States,  etc.    8vo,  illustrated,  cloth    250 


• Coignet  Beton  and  other  Artificial  Stone.    9  plates,  views, 

etc.    8vo,  cloth 2  50 

GOODEVE  (T.  M.)    A  Text-Book  on  the  Steam-Engine.     143 

illustrations.     I2mo,  cloth V ?  oo 

GORDON  (J.  E.  H.)   Four  Lectures  on  Static  Induction.    lamo, 

cloth 80 


6  D.  VAN  NOSTRAND'S  PUBLICATIONS. 

GRUNER  (M.  L.)  The  Manufacture  of  Steel.  Translated 
from  the  French,  by  Lenox  Smith,  with  an  appendix  on  the 
Bessemer  process  in  the  United  States,  by  the  translator. 
Illustrated.  8vo,  cloth $350 

xxALF-HOURS  WITH  MODERN  SCIENTISTS.  Lectures 
and  Essays.  By  Professors  Huxley,  Barker,  Stirling,  Cope, 
Tyndall,  Wallace,  Rpscoe,  Hvfgina,  Lockyer,  Youi.g, 
Mayer,  and  Reed.  Being  the  University  Series  bound  up. 
With  a  general  introduction  by  Noah  Porter,  President  of 
Yale  College.  2  vols  izmo,  cloth,  illustrated 2  50 

HAMILTON  (W.  G.)  Useful  Information  for  Railway  Men 
Sixth  edition,  revised  anu  enlarged  562  pages,  pocket  form. 
Morocco,  gilt 200 

HARRISON  (W.  B.)  The  Mechanic's  Tool  Book,  with  Prac- 
tical Rules  and  Suggestions  for  Use  of  Machinists,  Iron- 
Workers,  and  others.  Illustrated  with  44  engravings. 
I2mo,  cloth i  50 

HASKINS  (C.  H.)  The  Galvanometer  and  its  Uses.  A  Man- 
ual  for  Electricians  and  Students.  Second  edition.  I2mo, 
morocco i  50 

HENRICI  (OLAUS).  Skeleton  Structures,  especially  in  their 
application  to  the  Building  of  Steel  and  Iron  Bridges.  With 
folding  plates  and  diagrams,  fcvo,  cloth I  50 

HEWSON  (WM.)  Principles  and  Practice  of  Embanking 
Lands  from  River  Floods,  as  applied  to  the  Levees  of  the 
Mississippi.  8vo,  cloth 2  oo 

HOLLEY  (ALEX.  L.)  A  Treatiseon  Ordnance  and  Armor,  em- 
bracing descriptions,  discussions,  and  professional  opinions 
concerning  the  materials,  fabrication,  requirements,  capa- 
bilitie«,  and  endurance  of  European  and  American  Guns, 
for  Naval,  Sea-Coast,  and  Iron-Clad  Warfare,  and  their 
Rifling,  Projectiles,  and  Breech-Loading ;  also,  results  of 
experiments  against  armor,  from  official  records,  with  an 
appendix  referring  to  Gun-Cotton,  H&oped  Guns,  etc.,  etc. 
948  pages,  4Q3  engravings,  and  147  Tables  of  Results,  etc. 
evo,  half  roan 10  oo 

• Railway  Practice  American  and  European  Railway 

Practice  in  the  economical  Generation  of  Steam,  including 
the  Materials  and  Construction  of  Coal-burning  Boilers, 
Combustion,  the  Variable  Blast,  Vapoiization,  Circulation, 
Superheating,  Supplying  and  Heating  Fetd-wster?  etc., 
and  the  Adaptation  of  Wood  and  Coke-burning  Engines  to 
Coal-burning;  and  in  Permanent  Way,  including  Road-bed, 
Sleepers,  Rails,  Joint-fastenings,  Street  Railways,  etc.,  etc. 
Witn  77  lithographed  plates.  Folio,  cloth ..12  «o 

HOWARD  (C.  R.)  Earthwork  Mensuration  on  the  Basis  of 
the  Prismoidal  Formulae.  Containing  simple  and  labor- 
saving  method  of  obtaining  Prismoidal  Contents  directly 


D.    VAN   NOSTRAND  S    PUBLICATIONS.  7 

from  End  Areas.  Illustrated  by  Examples,  and  accom- 
panied by  Plain  Rules  for  Practical  Uses.  Illustrated.  8vo, 
cloth  $l  50 

INDUCTION-COILS.  How  Made  and  How  Used.  63  illus- 
trations. i6mo,  boards 50 

ISHERWOOD  (B.  F.)  Engineering  Precedents  for  Steam  Ma- 
chinery. Arranged  in  the  most  practical  and  useful  manner 
for  Engineers.  With  illustrations.  Two  volumes  in  one. 
8vo,  clolh 230 

JANNETTAZ  (EDWARD).  A  Guide  to  the  Determination  of 
Rocks:  being  an  Introduction  to  Lithology.  Translated 
from  the  French  by  G.  W.  Plympton,  Professor  of  Physical 
Science  at  Brooklyn  Polytechnic  Institute.  I2mo,  cloth....  i  50 

JEFFERS  (Capt.  W.  N.,  U.  S.  N.)  Nautical  Surveying.  Illus- 
trated with  9  copperplates  and  31  wood-cut  illustrations. 
8vo,  cloth 500 

JONES  (H.  CHAPMAN).  Text-Book  of  Experimental  Or- 
ganic Chemistry  fo-  Students.  i8mo,  cloth I  oo 

JOYNSON  (F.  H.)  The  Metals  used  in  Construction:  Iron, 

Steel,  Bessemer  Metal,  etc.,  etc.  Illustrated.  iamo,  cloth.  75 

Designing  and  Construction  of  Machine  Gearing.  Illus- 
trated 8vo,  cloth , 2  oo 

KANSAS  CITY  BRIDGE  (THE).  With  an  account  of  the 
Regimen  of  the  Missouri  River,  and  a  descnption  of  the 
methods  used  for  Founding  in  that  River.  By  O.  Chanute, 
Chief-Engineer,  and  George  Morrison,  Assistant-Engineer. 
Illustrated  with  five  lithographic  views  and  twelve  plates  of 
plans.  410,  cloth 6  OO 

KING  (W.  H.)  Lessons  and  Practical  Notes  on  Steam,  the 
Steam-Engine,  Propellers,  etc.,  etc  ,  for  young  Marine  En- 
gineers, Students,  and  others.  Revised  by  Chief-Engineer 
J.  W.  King,  U.  S.  Navy.  Nineteenth  edition,  enlarged. 
8vo,  cloth 2  oo 

KIRKWOOD  (JAS.  P.)  Report  on  'the  Filtration  of  River 
Waters  for  the  supply  of  Cities,  as  practised  in  Europe, 
made  to  the  Board  of  Water  Commissioners  of  the  City  of 
St.  Louis.  Illustrated  by  30  double-plate  engravings.  410, 
cloth 1500 

LARRABEE  (C.  S.)  Cipher  and  Secret  Letter  and  Telegra- 
phic Code,  with  Hogg's  Improvements.  The  most  perfect 
secret  code  ever  invented  or  discovered.  Impossible  to  read 
without  the  key.  i8mo,  cloth I  oo 

LOCK  (C.  G.),  WIGNER  (G  W.),  and  HARLAND  (R.  H.) 
Sugar  Growing  and  Refining.  Treatise  on  the  Culture  of 
Sugar- Yielding  Plants,  and  the  Manufacture  and  Refining  of 
Cane,  Beet,  and  other  sugars.  8vo,  cloth,  illustrated 12  oo 


8  D.  VAN  NOSTRAND'S  PUBLICATIONS. 

LOCKWOOD  (THOS.  D.)  Electricity.  Magnetism,  and  Elec- 
tro-Telegraphy. A  Practical  Guide  for  Students,  Operators, 
and  Inspectors.  8vo,  cloth , $2  s,o 


LORING  (A.  E.)  A  Hand-Book  on  the  Electro-Magnetic  Tele- 
graph. Paper  boards 50 

Cloth 75 

Morocco I  oo 

MACCORD  (Prof.  C.  W )  A  Practical  Treatise  on  the  Slide. 
Valve  by  Eccentrics,  examining  by  methods  the  action  of 
the  Eccentric  upon  the  Slide-Valve,  and  explaining  the  prac- 
tical processes  of  laying  out  the  movements,  adapting  th* 
valve  for  its  various  duties  in  the  steam-engine.  Second  edi- 
tion Illustrated,  ato,  cloth 250 

McCULLOCH  (Prof.  R  S.)  Elementary  Treatise  on  the  Me- 
chanical Theory  of  Heat,  and  its  application  to  Air  and 
Steam  Engines.  8vo,  cloth 3  50 

MERRILL  (Col.  WM.  E  ,  U.  S.  A.)  Iron  Truss  Bridges  for 
Railroads.  1  he  method  of  calculating  strains  in  Trusses, 
with  a  careful  comparison  of  the  most  prominent  Trusses,  in 
reference  to  economy  in  combination,  etc.,  etc.  Illustrated. 
4to,  cloth •; 500 

MICHAELIS  (Capt.  O.  E.,  U.  S.  A.)  The  Le  Boulenge 
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